I think I'll be doing this:
Crystal clear cube with change bag (takes 30 seconds as an opener)
Disappearing card case with invisible deck
Strat-O-sphere (4-5 minute routine)
I'll maybe cut fiber optics depending on the time
NO effect take 30 seconds! are you a "trick monkey" or are you a magician?
I don't really think you can just say that a 30 second trick makes you a "trick monkey" and not a magician. You haven't seen the effect so you really have no reason to judge the trick based on its time. I recently saw David Copperfield's show and his opener with his appearance lasted about 30 seconds, but no one in the audience could have said that it wasn't a good trick because it's short.
Plus, many great magicians have agreed that you must vary the time of the effects in your show. One 30 second trick in the show isn't gonna ruin a show or make the audience think that he's not a magician.
Spinbaby, remember to add entertainment value in all of your effects, regardless of the time it takes to perform them. Make the trick more entertaining than the effect itself.
And remember that everyone has a different character, so don't just do what someone else, or even I, say. 30 second tricks may not work for Paddy because of his presentation-focused magic, but it may work for you. No matter the character you have, make sure that it entertains the kids because that's all that really matters. It doesn't matter how you entertain them, it just matters that you entertain them.