I have a site using Joomla 2.5.4 and DT Register2.7.17. We still use JEvents with DT Register for various reasons but we have a time sync issue.
When linking a DT Reg event to a JEvents calendar item, the time auto-populates 3 hours off. Even both DT and JEvents are set to the same time zone. So for example if a event is scheduled in Jevents for 4 PM to 5 PM, when you add the event to DT Register and link it to the Jevent item, the time fields auto-populate the event as 1 PM to 2 PM.
While we can manually change the time before we save the event in DT Reg. Once it's saved the first time, the time fields are locked. So if a staff member misses the time sync issue and saves before they manually correct the time error, their only recourse is to delete the entire event in DT and recreate it.
I have seen this issue before, but you should update to latest versions of Joomla and DT Register. If the issue remains, post again. They won't (can't) support old versions - these things may have been fixed.
I'm having exactly the same issue with the most current version of DT Register and with Joomla 2.5.9. But, in my case, the time is off by only 1 hour.
I thought at first perhaps it was a Daylight Savings Time issue, but that is clearly not the case. Please let me know what additional information you need and I will try to supply it.