Yeah you must have tried the trade as credit, so for credit anything above 30 will bring benefit(but robinhood again dont allow this) you will get an error on robinhood that you cant get credit of more than the spread itself.
That is a good idea if I understand what you are talking about. When market it at a low point (determined by either 10m or 60m chart), put on the bull call spread side of the box. Then when market peaks out, put on the bear put spread to complete the box.