Ok,ok ok. So your laptop is on for that long, not the game. That makes much more sense. I thought you were one of those types that keeps WoW open and running for 48hr+ straight.
But now I see the issue. So your right on pinging the router's gateway and not going by any latency readouts from the game. The thing is, I can't think of anything off the top of my head that would cause that. The highest random factor in regards to wireless would be the group key interval, which by default is 3600 seconds, or 1 hr, but your stretch of time is longer then that. Some things you can try
1. Try a different laptop if you have one.
2. Try keeping it wired for a couple days, see if it happens then.
3. Go to the forums for your wireless adapter, ask there.
4. Try disabling the security on your router for a day or two.
If its the same with encryption on or off, I bet my hat its some setting, or driver issue with your wireless NIC. That would be further confirmed by trying a different laptop or going wired. Sorry couldnt really be of more help, its just most outside of the kind of problems we deal with here. Good luck.