Dealer in sandy springs Georgia. I've have good luck withem over 15 years of multiple mustangsOn the first page of my extended warranty, it says the following: "I agree to maintain the covered vehicle in accordance with the manufacturer's stated periodic maintenance recommendations as a condition of receiving coverage under this Agreement, except as otherwise provided by law."
In order to maintain any warranty, you have to show reasonable proof you've followed the prescribed maintenance schedule for your vehicle. Photos, log book, receipts, Ford Pass App, etc. Do you have to do the 5-year service all in one go? IMO, no. But you do have to accomplish and document each of those individual actions in some way. Who does the work is up to you.