Cookie Question

I've run into something rather odd with cookies today. I'm working with this admin section on a site and I'm setting a cookie that is supposed to be good for one hour. So in the cookie I have time()+3600 and all was well or that was until someone fired up IE. It seems that IE refused to set the cookie. After much swearing at IE, I found that if I set it to time()+7200 the cookie would be set. Not if that wasn't odd enough, in Firefox if I logged in at 6PM the cookie said it would expire at 8PM which is correct. However, when I logged in via IE at 6PM it said the cookie would expire at 23:00 hours (11PM for those who don't know)...so my question is...why is this happening and why does IE do this? I checked in Opera, Mozilla and Netscape and they all work the same as Firefox.....