I don't know about the inner workings of this site but I've been at other sites where we could predict that at certain times the server would be busy performing certain kinds of housekeeping (backups, cleanups, database indexing, notifications or whatever) so everything else would be slow.

It's also possible that the server might bog down when many members are active (reading or posting) at the same time.

I'm pretty much used to the normal speed of this site. At various times I've noticed delays (sometimes around this time of night, sometimes in late morning), but usually when that happens I just try again -- right away or a little later. If a delay happens while I'm trying to post something, I do copy-paste the text and save it in a file in case it should disappear on me. I don't think I've ever actually lost a post here, though.