yep, what beesly said. if the park opens at 9, the welcome show will probably start around 8:40, and the crowd will be walked in at the same time. you could always ask if you can go in early, but you should be prepared for a 'no' (it would be very unusual if you were let in early)
I would suggest standing back a bit so you can see the welcome show and walk leisurely down Main Street towards CP (since you aren't dashing to get to a busy attraction).