The BB can live a long time in a empty tank

As long as your nitrites are 0 ppm and your nitrates are not very high, your good to start stocking.

If you have algae in the tank, then I would suggest to start with some of your cleaning crew. If not, you could add your first fish

No need to rush stocking your tank tho, your live rock and BB will remain prefectly fine for many weeks to come in a empty tank.

Congrats on cycling your first marine tank