diff --git a/source/blender/blenkernel/BKE_scene.hh b/source/blender/blenkernel/BKE_scene.hh
index 7b6986ada01..2273ca70e50 100644
--- a/source/blender/blenkernel/BKE_scene.hh
+++ b/source/blender/blenkernel/BKE_scene.hh
@@ -138,7 +138,7 @@ const char *BKE_scene_find_marker_name(const Scene *scene, int frame);
  */
 const char *BKE_scene_find_last_marker_name(const Scene *scene, int frame);
 
-int BKE_scene_frame_snap_by_seconds(Scene *scene, double interval_in_seconds, int frame);
+float BKE_scene_frame_snap_by_seconds(const Scene *scene, double interval_in_seconds, float frame);
 
 /**
  * Checks for cycle, returns true if it's all OK.
diff --git a/source/blender/blenkernel/CMakeLists.txt b/source/blender/blenkernel/CMakeLists.txt
index 8e1dee7613a..c3fdc0bfddb 100644
--- a/source/blender/blenkernel/CMakeLists.txt
+++ b/source/blender/blenkernel/CMakeLists.txt
@@ -814,6 +814,7 @@ if(WITH_GTESTS)
     intern/main_test.cc
     intern/nla_test.cc
     intern/path_templates_test.cc
+    intern/scene_test.cc
     intern/subdiv_ccg_test.cc
     intern/tracking_test.cc
     intern/volume_test.cc
diff --git a/source/blender/blenkernel/intern/scene.cc b/source/blender/blenkernel/intern/scene.cc
index 39ca8ecef6b..c8ce63e217e 100644
--- a/source/blender/blenkernel/intern/scene.cc
+++ b/source/blender/blenkernel/intern/scene.cc
@@ -2306,14 +2306,19 @@ const char *BKE_scene_find_last_marker_name(const Scene *scene, int frame)
   return best_marker ? best_marker->name : nullptr;
 }
 
-int BKE_scene_frame_snap_by_seconds(Scene *scene, double interval_in_seconds, int frame)
+float BKE_scene_frame_snap_by_seconds(const Scene *scene,
+                                      const double interval_in_seconds,
+                                      const float frame)
 {
-  const int fps = round_db_to_int(scene->frames_per_second() * interval_in_seconds);
-  const int second_prev = frame - mod_i(frame, fps);
-  const int second_next = second_prev + fps;
-  const int delta_prev = frame - second_prev;
-  const int delta_next = second_next - frame;
-  return (delta_prev < delta_next) ? second_prev : second_next;
+  BLI_assert(interval_in_seconds > 0);
+  BLI_assert(scene->frames_per_second() > 0);
+
+  const double interval_in_frames = scene->frames_per_second() * interval_in_seconds;
+  const double second_prev = interval_in_frames * floor(frame / interval_in_frames);
+  const double second_next = second_prev + ceil(interval_in_frames);
+  const double delta_prev = frame - second_prev;
+  const double delta_next = second_next - frame;
+  return float((delta_prev < delta_next) ? second_prev : second_next);
 }
 
 void BKE_scene_remove_rigidbody_object(Main *bmain, Scene *scene, Object *ob, const bool free_us)
diff --git a/source/blender/blenkernel/intern/scene_test.cc b/source/blender/blenkernel/intern/scene_test.cc
new file mode 100644
index 00000000000..965f0855cf4
--- /dev/null
+++ b/source/blender/blenkernel/intern/scene_test.cc
@@ -0,0 +1,44 @@
+/* SPDX-FileCopyrightText: 2025 Blender Authors
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "BKE_scene.hh"
+
+#include "DNA_scene_types.h"
+
+#include "testing/testing.h"
+
+namespace blender::bke::tests {
+
+TEST(scene, frame_snap_by_seconds)
+{
+  Scene fake_scene = {};
+
+  /* Regular 24 FPS snapping. */
+  fake_scene.r.frs_sec = 24;
+  fake_scene.r.frs_sec_base = 1.0;
+  EXPECT_FLOAT_EQ(48.0, BKE_scene_frame_snap_by_seconds(&fake_scene, 1.0, 47));
+  EXPECT_FLOAT_EQ(48.0, BKE_scene_frame_snap_by_seconds(&fake_scene, 1.0, 49));
+  EXPECT_FLOAT_EQ(48.0, BKE_scene_frame_snap_by_seconds(&fake_scene, 1.0, 59));
+  EXPECT_FLOAT_EQ(72.0, BKE_scene_frame_snap_by_seconds(&fake_scene, 1.0, 60));
+  EXPECT_FLOAT_EQ(9984.0, BKE_scene_frame_snap_by_seconds(&fake_scene, 2.0, 10000.0));
+
+  /* 12 FPS snapping by incrementing the base. */
+  fake_scene.r.frs_sec = 24;
+  fake_scene.r.frs_sec_base = 2.0;
+  EXPECT_FLOAT_EQ(48.0, BKE_scene_frame_snap_by_seconds(&fake_scene, 1.0, 47));
+  EXPECT_FLOAT_EQ(48.0, BKE_scene_frame_snap_by_seconds(&fake_scene, 1.0, 49));
+  EXPECT_FLOAT_EQ(48.0, BKE_scene_frame_snap_by_seconds(&fake_scene, 1.0, 53));
+  EXPECT_FLOAT_EQ(60.0, BKE_scene_frame_snap_by_seconds(&fake_scene, 1.0, 54));
+  EXPECT_FLOAT_EQ(9996.0, BKE_scene_frame_snap_by_seconds(&fake_scene, 1.0, 10000.0));
+
+  /* 0.1 FPS snapping to 2-second intervals. */
+  fake_scene.r.frs_sec = 1;
+  fake_scene.r.frs_sec_base = 10.0;
+  EXPECT_FLOAT_EQ(48.0, BKE_scene_frame_snap_by_seconds(&fake_scene, 2.0, 48.0));
+  EXPECT_FLOAT_EQ(48.0, BKE_scene_frame_snap_by_seconds(&fake_scene, 2.0, 48.1));
+  EXPECT_FLOAT_EQ(48.2, BKE_scene_frame_snap_by_seconds(&fake_scene, 2.0, 48.2));
+  EXPECT_FLOAT_EQ(10000.0, BKE_scene_frame_snap_by_seconds(&fake_scene, 2.0, 10000.0));
+}
+
+}  // namespace blender::bke::tests
diff --git a/source/blender/blenloader/intern/readfile.cc b/source/blender/blenloader/intern/readfile.cc
index 304395ad168..83d7c1bb7c3 100644
--- a/source/blender/blenloader/intern/readfile.cc
+++ b/source/blender/blenloader/intern/readfile.cc
@@ -3501,6 +3501,11 @@ static void do_versions(FileData *fd, Library *lib, Main *main)
      * later during 5.0 development process. */
     version_system_idprops_nodes_generate(main);
   }
+  if (!MAIN_VERSION_FILE_ATLEAST(main, 500, 110)) {
+    /* Same as above, but children bones were missed by initial versioning code, attempt to
+     * transfer idprops data still in case they have no system properties defined yet. */
+    version_system_idprops_children_bones_generate(main);
+  }
 
   if (G.debug & G_DEBUG) {
     char build_commit_datetime[32];
diff --git a/source/blender/blenloader/intern/versioning_500.cc b/source/blender/blenloader/intern/versioning_500.cc
index d4a6eee850c..1b8c33b1cfb 100644
--- a/source/blender/blenloader/intern/versioning_500.cc
+++ b/source/blender/blenloader/intern/versioning_500.cc
@@ -130,8 +130,16 @@ void version_system_idprops_generate(Main *bmain)
     for (BoneCollection *bcoll : armature->collections_span()) {
       idprops_process(bcoll->prop, &bcoll->system_properties);
     }
-    LISTBASE_FOREACH (Bone *, bone, &armature->bonebase) {
+    /* There is no way to iterate directly over all bones of an armature currently, use a recursive
+     * approach instead. */
+    auto process_bone_recursive = [](const auto &process_bone_recursive, Bone *bone) -> void {
       idprops_process(bone->prop, &bone->system_properties);
+      LISTBASE_FOREACH (Bone *, bone_it, &bone->childbase) {
+        process_bone_recursive(process_bone_recursive, bone_it);
+      }
+    };
+    LISTBASE_FOREACH (Bone *, bone_it, &armature->bonebase) {
+      process_bone_recursive(process_bone_recursive, bone_it);
     }
   }
 }
@@ -145,6 +153,29 @@ void version_system_idprops_nodes_generate(Main *bmain)
   }
   FOREACH_NODETREE_END;
 }
+/* Separate callback for non-root bones, because they were missed in the initial implementation. */
+void version_system_idprops_children_bones_generate(Main *bmain)
+{
+  LISTBASE_FOREACH (bArmature *, armature, &bmain->armatures) {
+    /* There is no way to iterate directly over all bones of an armature currently, use a recursive
+     * approach instead. */
+    auto process_bone_recursive = [](const auto &process_bone_recursive, Bone *bone) -> void {
+      /* Do not overwrite children bones' system properties if they were already defined by some
+       * scripts or add-on e.g. */
+      if (bone->system_properties == nullptr) {
+        idprops_process(bone->prop, &bone->system_properties);
+      }
+      LISTBASE_FOREACH (Bone *, bone_it, &bone->childbase) {
+        process_bone_recursive(process_bone_recursive, bone_it);
+      }
+    };
+    LISTBASE_FOREACH (Bone *, bone_it, &armature->bonebase) {
+      LISTBASE_FOREACH (Bone *, bone_child_it, &bone_it->childbase) {
+        process_bone_recursive(process_bone_recursive, bone_child_it);
+      }
+    }
+  }
+}
 
 static CustomDataLayer *find_old_seam_layer(CustomData &custom_data, const blender::StringRef name)
 {
diff --git a/source/blender/blenloader/intern/versioning_common.hh b/source/blender/blenloader/intern/versioning_common.hh
index 0f83f2e48f3..0dd284787e3 100644
--- a/source/blender/blenloader/intern/versioning_common.hh
+++ b/source/blender/blenloader/intern/versioning_common.hh
@@ -218,6 +218,7 @@ bNode *version_eevee_output_node_get(bNodeTree *ntree, int16_t node_type);
  */
 void version_system_idprops_generate(Main *bmain);
 void version_system_idprops_nodes_generate(Main *bmain);
+void version_system_idprops_children_bones_generate(Main *bmain);
 
 bool all_scenes_use(Main *bmain, const blender::Span<const char *> engines);