Hard to see how a problem with the setup could cause a problem after 10-15 hours. I would guess that the problem there is with your ISP or maybe the router itself. I used to have to turn the power to the router off for a few seconds and let it re-connect, every now and then, under either Windows or linux.
You might want to check if all the right LEDs are lit on your router when that happens. Mine has LEDs for power, wlan, adsl and ppp when it is working. It would also be useful to know if you can ping your router.
Mine is working fine now, see my question http://www.vectorlinux.com/forum2/index.php?topic=3700.0
although that doesn't include dhcp.
You will get clues from:
can you ping an outside address, e.g. your dns server?
can you ping the router as above?
what is the output of
# route -n
what is the output of iwconfig?
Probably more of a networking question