There’s not a waiting period, but what has happened here is that Micro.blog keeps track of when searches on a Mastodon server are repeatedly failing, and it temporarily stops looking up users from that server. That is what has happened here.
I’ve cleared the error manually and that user should be discoverable now.
I think we’ll need to tweak our logic here so that it recovers from these errors more quickly. I added it back when mastodon.social was getting hit by a denial-of-service attack.