I had it set to localtime instead of UTC, which for me is -5 hours. Caused me a bit of grief earlier today after making a new post that started out already five hours old!
It seems like a real pickle though. What if I set my time to a year in the future and make a post? Would that post stay at the top of new all year? I guess lemmy should use the received date rather than what is sent but that could be problematic when things are bogged down or having federation issues.