DD-WRT loses time

Hello everybody,

I have a Buffalo DSL-router with new firmware by DD-WRT flashed on it. I enabled NTP to time.windows.com (which is always reachable in my experience) but for some reason it does not synchronize the time after a reboot immediately. When I restart the router, it says 'Jan 01' and does not update for several hours.

Does anybody know, how to fix this? It is crucial for me, since it forwards message via syslog to a server, and reports on syslog data are extremely unreliable because events come in with the wrong time/date.

The firmware is: "Firmware: DD-WRT v24-sp1 (07/27/08) vpn"

Thank you very much for any advice!
Chris