Described me to a T! ;-)
Seriously, most kids are early risers -- so perforce most parents are too! And if HT is a long distance, it sounds as if there will probably be a TLM closer in the Boston area that they'll prefer regardless of the time. I think 8:30 or 9:00 sounds great! I don't have kids, but it might take me an hour to get there. (When it was at noon, because of the bus schedule I could either be 20 minutes early or 10 minutes late.)
Well, I hope you forgive me for being a bit utilitarian about this, but I would lobby for a later time (10 AM would probably be ideal, but it would directly conflict with the existing N.O. Mass for the Germans) solely because I think it would produce the largest number of people. And boosting attendance by the greatest possible amount is the only thing that can save this church from ultimate closure. Seeing all of the logistics some of the folks with large families already undergo to trek across a good chunk of the archdiocese to get to the TLM, and formerly dealing with this stuff myself (albeit with only one small child) in my 53 mile ride to HT in the 1990’s, I can see that not too many would be fans of anything earlier than 10 AM. Since they are, as you know, the largest demographic group attending the TLM at Holy Trinity or at Mary Immaculate, their maximum possible participation is no small matter.
Of course, in a “perfect world” dealing with the Extraordinary Form, the FSSP, or ICK or a diocesan priest dealing with Holy Trinity as a personal parish for the TLM would be able to schedule an 8, 10 AND 12 o’clock TLM without any interference from certain individuals a few blocks west at 1400 Washington Street! But we know THAT ain’t gonna happen any time soon! ;-)