Actually, this whole idea of hitting the same page on the web server 2x per second, 24x7 sounds like pretty impolite behavior. If that was happening to me and I was able to figure it out, I would stop talking to your IP address. Update:and I would do my best to blacklist you with other servers!..No I wouldn't be that nasty, but you would be on my server's "bad boy" list.

All of the algorithms for doing the date stuff are fast enough for what you "need". And actually I don't even see the need for comparisons, if the date changed since then last access then, it most likely got bigger (ruling out some time goof at the sending end).