Timestamps not displaying correctly

For some reason, there have been issues with anything involving time for me on this site (times when people were last online, when my posts were sent, etc.). For example, if I check to see if someone's online at noon, and their profile says they last visited the site at ten am, if I check later that day, it'll say they were last online at eleven am (before I first checked, but a different result nonetheless), or one of the posts that I sent at around four thirty today is marked as being sent a little after three (which would be impossible, because I hadn't even started writing it at that time).

None of this seems to follow any particular pattern (for example, the timestamps aren't all off by an hour, but rather, the times vary), and I can't think of any logical reason why this is happening (I could understand a lag in the time when something might have sent, but instead, it's recorded as having sent before it actually was).

Has this happened to anyone else, or does anyone have any insights or suggestions?