Split stay - onsite and offsite

[MouseMum]

I have 2 weeks booked at the Poly for August, but am now considering possibly cancelling the last week and staying in a house in Windsor Hills instead for that time. We will have 8-day park tickets and want to spread out our days to have break days in between, so this means I'll likely be doing at least 3 park days while offsite. How does FP booking work for this arrangement? Is it 60 days for the onsite days and 30 days for offsite? And how would I book the dates I want to use as park days? I have only done this when staying onsite. The offsite experience would be completely new. TIA!