I can't help you with your question. I'm sure there are folks here that can.

Another great poultry forum is The Coop:

http://www.the-coop.org/cgi-bin/UBB/ultimatebb.cgi

I have had them hatch a day early but they usually take 21 days like the big girls.

Only difference is size; that creates the greatest problem when hatching large fowl and bantams together, The lf chicks may trample the bantam chicks. Some strains do hatch earlier than others but that can be said for the lf also.
A soloution can be to put the bantam eggs in a wire basket inside the incubator, I do that for pedigree reasons to kep them seperate.