Wow I'm in the exact same boat lol. I asked my advisor about this.
For schools that your MCAT is competitive for, they usually will push you application forward without waiting for the 2nd MCAT score. For schools where your MCAT is a bit on the lower end, they will generally still send secondaries if the rest of your application is good/ not-screened. However, they will probably wait for it before an interview offer. For schools where your MCAT is below 10%, they will probably wait for the score, if not, they may just straight up reject you XD
Of course, this varies from school to school, but I thought it was helpful.
Good luck June 21st =)