I would like to re-visit my last server, but I don’t want to re-set the decay timer, so I’d like to know how long I’ve been away or, alternatively, how long I’ve been on the new server (since I changed the same day). Is this possible?
No, it’s not. The client does not store that information and there’s no protocol for asking the server to tell you. The best you can do is to ask – outside of the game – some other player you know on that server.
You say you’re not interested in refreshing your base. Is there the possibility that you could tear it down instead, rather than just letting it decay?
Yes, I could tear it down. It’s in a pretty remote location on a low pop Siptah, and my friends there knew I was leaving and will probably loot it after it’s decayed, no one asked me to tear it down. On more crowded EL servers when I had a primo location, I would tear down before leaving. I made a different choice this time. I don’t like contributing to urban blight, but this doesn’t really seem to qualify.
So I have made a list of every single character I have made, their name, level and some notes on what happened on the server.
This is the only way I have been able to keep track.
This is also what I would suggest. I keep a notebook for various games and it helps me remember what I was doing and where.