The best solution for “last follower” is to use EventSub
Which has a followers topic, so you can recieve an instantish notification when you get a new followers.
Alternatively you can call
With a call similar to
https://api.twitch.tv/helix/users/follows?to_id=YOURID&first=1
Which will return the most recently follower.
if you need “followers since x time”
https://api.twitch.tv/helix/users/follows?to_id=YOURID&first=100
and paginate till you hit a followed_at older than the time you are after