Imo

i spongeball routine i do i can make it go for 2 minutes a;; the way up to 10 minutes, it all depends on your patter and how you present the trick, you want to stay long enough so they can enjoy it (about 3 minutes), but not to long so that you will start to pester them (unless they love it and you)

I start off showing 2 spongeballs and just mention for kids they are like a clowns nose for red nose day but made of sponge, or for a adults you say i have to meatballs here or somehting and they will usually make a stupid joke likes let me touch your balls or somehting stupid

Then i start with a confusing spongeball line. and i make 2 in their hand appear, i then do that again, then i go into a 2 in the hand 1 in the pocket and if i feel good ill start joking around doing a 2 in the hand one in the pocket but appearing novelty Massive spongeballs in my hand or minature ones and that always gets a good laugh and will confuse them.

Finally do anyhting effects or anything (example - 2 in the hand 1 in the pocket) to make them all vanish, and done