You can add fish when you have 0 ammonia, 0 nitrites, and ~40 ppm
nitrates. How big is your tank? The cycle takes as long as how much of a bacteria source you have. What do you have in there?
After I first cycled my tank, I added 9 SMALL fish at once and I've never had a problem since. Now I have 13.
EDIT: Upon re-reading maybe you've already cycled? If so, you shouldn't have to wait to add a new fish. If you have a sufficient biofilter, you should be fine.
1 yoyo loach, 2 polkadot loaches, 6 cherry barbs, 2 turquoise rainbows, 1 chinese algae eater, 2 harlequin rasboras; java fern, java moss, hornwort, Asian ambulia