Not perfectly on time; possibly somewhat late, but no harm is done as a result. The implication is that there is no need to be exactly on time, and starting a little late is acceptable.
The term comes from Jewish culture, which is often relaxed about punctuality.
When an event is schedule to take place at 2:00 Jewish time, it could be at 2:05, 2:12, 2:15, or even 2:35, and everyone is satisfied.
The wedding will start at 6:00 PM Jewish time.
We will meet in the lobby at 4:30 Jewish time.