Solution is quite simple.
Since your student visa is valid until January, you can postpone your FLR(M) application until your return from the US in October.
Or if you prefer, you can apply for FLR by same-day premium service straight after your wedding. Appointments are released 6 weeks in advance and scouring the whole country, you should be able to find a time and date to suit. Your biometrics are taken during the appointment. You usually get your biometric residence permit (don't leave UK without it!) within 5 days, but allow up to 10 days.
If you are going to delay your FLR application till October, then I suggest you carry some supporting documents when going through UK borders, such as marriage certificate, bank statement showing sufficient funds and firm intention to apply for FLR (get a printout of your same-day appointment). But only show them when asked, don't volunteer. Answer questions truthfully.