Tube Amp out of Bias-what does it sound like?

In a nutshell, if they are biased too low the sound will be groggy and not very involving, too high will sound better but you will put additional wear on your tubes.

I agree with what Newbee and Philojet have said.
Out of bias does affect the sound. That being said, it is unwise to say to low or to high. To much room for confusion. Much more appropriate to say to cold or to hot. To cold there is not enough current in the output stage to work correctly. Sound will be buzzy, not clean etc.. To hot can sound very good (unless way to hot) but lots of drawbacks. Tubes wear out much to quickly, the whole system is stressed to much which isnt good.

How long should you wait after turn to check/adjust bias?

The initial bias setting is made when the amp has been on for a few minutes, usually after a tube change etc, and with the bias set at its minimum setting. Once that setting has been made let the amp run for an hour or so to warm up sufficiently then go back an check/reset the bias to the factory recommended settings. Unless you have a bad tube(s) or a poor amp these last setting should remain stable for at least a few months. Good to watch bias, but no need to be anal about it. :-)