There are downsides to very low TTLs. I'd advise against them. Best practice is to set a high TTL, and as you plan to make a migration that involves DNS, set

There are downsides to very low TTLs. I'd advise against them. Best practice is to set a high TTL, and as you plan to make a migration that involves DNS, set a lower TTL so that when you make the change it propagates quickly. When done and all is stable, raise your TTL again. The longer your record is cached, the better off you are.