I also have an issue with the DIR-655 not keeping time. As I already have a ticket in for another issue, I have noticed that when my wireless it disabled (or turned off) the DIR-655 appears to keep time without an issue. But when the wireless is enabled (turned on) then it cannot keep time, or falls behind. Of course mine appears to want to reboot whenever it wants for about 30 minutes, our unless I remove power from the system.
I have the A2 ver and have updated the firmware to the current firmware (not willing to lose my router if something else goes wrong with it or I install the Beta firmware and it crashes).