Hashes of objects are computed in a few places, but objects are immutable once placed in the timeline, so they should not need to recompute hashes. These extra hashes make up a significant chunk of CPU overhead caused by the timeline.
These hashes do not make up a significant chunk of CPU in the new nontrivial test. I'll get around to this once larger performance issues have been resolved.
Hashes of objects are computed in a few places, but objects are immutable once placed in the timeline, so they should not need to recompute hashes. These extra hashes make up a significant chunk of CPU overhead caused by the timeline.