The gist of what I've been reading is that the Smuggler's Run line actually peaks in length in the first couple hours of opening and then tapers off, since a lot of people head for it at rope drop and there's no FP+ to keep the standby line long throughout the day. That being said, I generally don't like to put off rides if I have limited opportunities to experience them, since you never know when something's going to go down.
Check for openings the night before. Reservations have to be cancelled the day before to avoid a no-show fee, and it's fairly common for people to change their mind last minute and drop reservations right before that deadline. If that level of uncertainty is going to make planning this unenjoyable, I'd use the Touring Plans tool mentioned above and/or make alternate plans.