API endpoints will always be a little behind by about 30 seconds to even longer (depending on load I believe, few minutes isn’t that uncommon I think.)
If you are building a follower notification system, then a common practice is, when an API call is done and new followers found, announce them evenly between the time the call is done till the time the next call is done.
I also tried on my end to see if there was a difference between pulling followers via /streams/ or /channels/ but both update at about the same time.