After investigating the in game timer, it measures time in minutes:seconds:thirds format where the "thirds" part is a unit equal to 1/60 second. Existing runs that are listed as hh:mm:ss:ms should probably be fixed to show actual millisecond counts.

I've spent a few minutes looking into what to call the "thirds" unit and it seems like ["third", "jiffy", "tick"] are varyingly accepted.

If I understand correctly, you’re saying the in game timer lists frames and goes from .00 to .59, instead of using centiseconds from .00 to .99?

It appears that way. I've reconfirmed just now as I watch a new run's clip rendering in blender. The third unit runs from :00 to :59.