Lots of variables to take into account here. First what is sizeable? How are growing conditions? Fertilization regime?

I know of some Dutch nurseries that can get a saleable/sizeable plant from cuttings in about 2,5 to 3 years. This is of course under very professional conditions with heavy fertilization. The pot size is usually 2 or 2,5 liters (you have to do the gallon conversion yourself!).

But note that it is not that easy to get an azalea cutting rooted under amateur conditions. It is not impossible but success rate may be low.

Frankly, I'd just purchase a gallon size or 2-gal. size plant. Much faster! A few azaleas that I started from cuttings took about 4 years before they even made a dent in the landscape.