Hopefully you get this in time, but it'll would be better to spend the extra 30 min (if that) to make the drive to Big Bear. I think it a much better hill to ride with better snow conditions typically. I have yet to be to either this season, but that's what I've known to be true in the past. Either place is still fun ride.
Can't answer your first two questions (never rented at mt. high either). But your drive time all depends on what part of LA your leaving from. I'd suggest to go early as possible, so you can avoid most of the traffic. Took me an hour last year coming from San Fernando Valley, but it was also a weekend without morning rush hour.