Cycling or not?

Dabbler, how long did it take to cycle that 120 Gallon. I am getting a 80 Gallon in the next month or 2 and I am doing a fishless cycle, thou I am also selling my 40 Gallon to my neighbor and I wanted to know how long it would take me (just a guesstimate to give to the neighbors till they can get the tank).
 
Is it possible to put the bacteria colony ahead of the fish load by adding a little ammonia to the tank after the tetras were in there? Im talking a very small amount just to have a little more ammo in there than the fish themselves would produce.
 
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