anything over 1/16" is too much. If you build carefully you should be able to consistently get a 1/64" gap. But with CA hinges apparently you have to deliberately give them a larger gap so they don't break. I don't use them because they are fundamentally wrong in how they work, but a lot of guys swear by them.

Anyway, if you seal the hinge line with iron-on film or clear packing tape, the gap doesn't matter much. However, a large gap also means control slop which sealing the hinge line won't eliminate.

Point being that a smaller gap is better, but planes with larger gaps still manage to fly.