>It appears to work the same as the global refresh button on the top. However a couple of times it displayed a couple of different messages, so I'm still not sure. The "since last login" time warp feature displays more messages than were displayed when I logged in - and they were messages that were never displayed before so it seems to resolve the issue of some messages "disappearing."

This is exact. I keep a last message ID at the time of the login and another one at every time you click on the global refresh (the two green arrows). So, it is a pointer in time. So, if you do "Since last login", it is everything since the last login and not only those messages you got at the login time. The same goes with the global refresh, with the use of the "Since last refresh".

The goal of the option is to allow you to go back in time from that time. I do not keep another point for to BETWEEN like. Basically, it is as the option says. It says "Since...". So, everything since that specific time will be retrieved. I made more tests on it today and it seems to work as usual.

Let me know if you need more information on the topic.