Transmission center's don't wait 24 hours before adding the ATF and letting the customer leave in their car. I don't think the Tranny place I went to even used Threebond, just silicon and mine isn't leaking.
Just be sure to clean the old silicon, threebond, whatever, off of the pan's sealing surface. As far as anything being tricky, I would put a dab in the bolt holes of the pan to keep it from leaking. Just run a 1/4" bead all the way around the pan mating surface and put a little in the bolt holes.
I'm not saying there aren't any gaskets for the auto tranny pan, but I haven't seen any, but nor have I looked. Having a second set of hands will help keep the sealer from being smeared and will allow you to put the bolts in easier. However, this isn't necessary because the pan is not that big and most people do it by themselves. Lastly, do you know the torque specs for the bolts and the tightening pattern? Get this info to keep from kinking the pan, say from tightening the bolts like -->|<--- if that makes sense. Usually start in the top middle, then tighten the bottom middle, and work your way out <--|-->. I'm sure this info is out there, but I'm at work now so I don't have time to search it up. Good luck.