The FP system now is more accommodating to guests who park hop yet many DISers don’t know about this info.
Guests don’t have to pre-book 3 FPs...if they only pre-book 1 (or 2 FPs), as soon as they enter the line for FP#1, they can immediately book the remaining ‘initial’ FPs at Park#2 and/or Park#3...including Tier 1 attractions.
From the FP FAQ ADDENDUM STICKY:
When_2 or less FP are booked for Park #1:
If you book fewer than three FP and once you scan the first FP from within the first park, you can at that point make FP selections for a different park, even if you still have a FP remaining in the first park.
This can be especially helpful for Tiered parks – if for example you wish to hit Epcot at rope drop, use only a Tier 1 FP and then still have 2 more FP for another park later in the day.
Additionally, there is no restriction on Tier requirements BETWEEN PARKS during one day. So if you use a Tier 1 at Epcot you can then book a second Tier 1 at HS immediately upon scanning – Also, you can even book your remaining two FP at two different parks if you would like!
NOTE: Splitting FP between parks or booking for another park CANNOT be done until the same day, AFTER you have already scanned your card/MB at the first FP Mickey head to “prove” to the system that you’re in a park.
You cannot book for 2 different parks in advance or even on the same day until you have scanned your first FP (not just entered the park).