The post merger code is accurate. XX:XX is the *server* time (time zone: EST/EDT) the person made a double post, which is why the "Previous post" time is supplied too.
The date isn't included (so you're unaware of what day each individual time applies to), and with each double post the "main" post's time is altered too...so I can see how that is confusing.
Hm, point taken. I might be mistakening this system with another I was working on... It does indeed take the time from the poster's settings and it isn't EST... I wonder why I added that then, hm.
Thanks for the bug report, much appreciated ! I'll look into it.