Tested on my level 20 thief acrobat rogue.
Bug reported.

The cooldown for improved uncanny dodge is 2 minutes, which is not stated in the description.

Description also states 50% for improved uncanny dodge instead of 60% from the release notes.

The counter for improved uncanny dodge has been removed, but the thief acrobat prestige still grants increased uses of improved uncanny dodges.

I can imagine that thief acrobats will have an increased duration and/or a reduced cooldown for improved uncanny dodge in the future.