Unless you're willing to put serious effort into growing rotifers for them, then you may never be ready. The larvae are planktonic, and will float away on the night of hatching. Sadly, they will become food for the tank.
I keep promising myself that I'll raise a clutch at some point, but haven't made the effort so far. In general, clowns will spawn every few weeks for many years.
A couple of good books on the subject:
Wilkerson
Hoff