The fix contains two parts: 1. Grease Pencil v3 now stores stroke `init_time` as a float attribute, it's not enough precisiton for unix timestamp. Now the time value is truncated to allow better precision. It's still stored in seconds. 2. The previous logic for calculating stroke gap time of the build modifier isn't correct, it used to only count two starting times as gap time. Now it's fixed with correct delta time. Pull Request: https://projects.blender.org/blender/blender/pulls/124350