The special-needs (tandem, trike, recumbent, etc.) starts are 84hr and 90hr only, starting 15 minutes or so before the first 'standard' group with that time limit.
There is never any problem with two brakes on the front wheel for upright trikes. Barry Parslow showed the way for trikies at PBP about 50 years ago and Jim Hopper has started 9 PBPs on trike, so they know the deal.