In this particular instance, if you upgrade to the newest firmware, it'll be the name thing as restoring it. IOW, you won't have to do two separate steps - the restore will put iOS 5.1 on your iPad.
Is your iPad on iOS 5.0.1 now? Is it working fine or do you need to restore it because it's not working? If its fine and you want to keep it jail broken, do nothing.
If your iPad is not working properly, what is making you think you need to restore it? Usually, a restore is the last thing a jail breaker wants to do because you lose the jail break. So, maybe you can describe what is happening, or not, to your iPad? Maybe we can help you fix the problem and save your jail break.
However, if it's not working and you've decided you need to restore it (which will be the same thing as upgrading it to the newest firmware), then follow the steps outlined here:
TUTORIAL - Failsafe method to restore the current version of IOS. Again, restoring it will put on iOS 5.1 on it and you will lose your jail break.
For this question:
Generally speaking, Apple stops signing firmware on their own schedule. Here lately, it's been about 24to 48 hours after the release of new firmware. The only thing to know is to watch for a new firmware release. Then, you wl know that it's only a short matter of time before Apple closes the window; they don't keep two firmware versions out for very long.
He some of this helps.
Marilyn