Taking this into consideration:
Parks With FP Tiering
A second Group 1 attraction in the same park can be scheduled only as a 4th FP or beyond. In other words, scheduling less than 3 FPs for a day in a tiered park is not a shortcut to getting a second Group 1 FP in the same park faster.
We will be arriving at HS at approximately 3 pm, and cannot arrive earlier. It will be our only day at HS. Our family would like to ride RNR and TSMM (both Tier A). I've booked a FP for 3-4 pm for RNR as the standby lines seem to be shorter than for TSMM. I did not book FPs for any Tier B attractions as the lines are all very short. Am I reading correctly that I must book and use all 3 FPs before being able to book an additional Tier A attraction? This seems silly...if so, I will book them prior to 3 pm and just let them lapse?