How to Reproduce:

1. set server timezone to Americas/Chicago (GMT-5)
2. set user timezone to Europe/Riga (GMT+2)
3. go to any trackable object (maniphest task or differential revision)
4. press Start Tracking Time link
5. submit the form

Then the error about incorrect time would be shown. Problem is that time in the error is 8h (timezone difference) larger than time what was entered by user.

Version: https://secure.phabricator.com/w/changelog/2016.15/

P.S.
I know that bug reports on prototype applications are not accepted, but this should be an easy fix.