All Nippon Airways (ANA) miles expire at the end of the 36th month from the date you earned the miles, with no option to extend the expiration date, unless you have ANA Diamond elite status.
For example, if you transferred 95,000 American Express Membership Rewards Points to ANA on March 15, 2021, those miles would expire on March 31, 2024, even if you transferred additional miles to ANA.
So you either to redeem your ANA miles before the deadline or you will lose your ANA miles.
Luckily, the flight on miles can occur after the mileage expiration as long as you book it before the miles expire.
ANA will extend your ANA miles due to expire between March 31, 2021 and August 31, 2021, if you register in advance.
However, the miles are only extended to September 30, 2021, so you will need to use your miles before then.