It starts from the day u purchase AppleCare+, not the day u bought your phone.
I have bought AppleCare+ many times and it always start on the date ac+ was purchased though it was always within the first 60 days.
And a few users also confirm it can be bought within 1 yr if u pass the check and it adds another 2 years of ac+ warranty for your devices.
https://www.apple.com/sg/support/products/iphone/
From Apple.
Enjoy two years of peace of mind when you buy AppleCare+ for iPhone.
Every iPhone comes with one year of hardware repair coverage through its
limited warranty and up to
90 days of complimentary technical support. AppleCare+ for iPhone extends your coverage to two years from your AppleCare+ purchase date
1 and adds unlimited incidents of accidental damage protection. Each incident is subject to a service fee of S$42 for screen or back glass damage, or S$148 for other accidental damage.
2 In addition, you’ll get 24/7 priority access to Apple experts by chat or phone through
getsupport.apple.com.