I have installed my instance over the fresh download of 5.1 core + required dependencies (acs-datetime, acs-events, notifications, categories, organizations, logger, and acs-mail-lite AFAIR). I suspect that your issue is in PG 7.3.4 -- there have been some changes to time/timestamp/etc. data types.
On a separate note, I am having problems logging in hours (but I have no problem changing percentage of completion), but can't post error message right now, as I am away from the other machine with OACS/PM instance.
One more note -- while installing 5.1 + deps, there were several times strange issues with the installer, whereby it would report an error -- but when looking at the logs no issues were recorded, albeit there were some extra messages. I have not marked them down, unfortunately. Will probably try to instantiate the same on another machine to see if it repeats, then would post them in bugtracker.