I don't think any of the pre-cons are recorded and available online. I myself have never attended the pre-cons, so cannot tell you how much time you will have to get other things done. Those that I know who have gone say it is a pretty full day.
As for registration, those registered for a pre-con get their TechEd registration done earlier on the Sunday the rest of the attendees. We cannot register till around 10:00 or 11:00 am on Sunday. According the schedule Hand-on -labs are open from 12 - 6pm and I think most take around around 45 min to complete.
But you should take some time to regroup before going to #theKrewe meet-n-greet Sunday night.