As Bart said, you will have time to make use of the warmers for both the practice session, and the race itself.

You can sign up the day of, at the track, but be sure to get there early enough to get the paperwork filled out, unload your bike, and be ready for Tech, prior to the classroom session. The Superstreet bikes will be going thru tech inspection immediately following the classroom session, so there will not be time to unload and prep your bike.