Set whatever you want, reboot using the reboot button in misc settings and your settings will save. Cutting the power will cause a loss of settings.
To fix your time (I have no idea why you'd want to do this anyway) go to time, click in the box that says "select time", click set and then update.
Ah, didn't know a reboot was needed for the settings to be retained. Based on what I've read here I thought you just need to tick enable cookies.
I like the router time to match my local time for troubleshooting, like my VPN disconnect issue.