Really depends on tank conditions and how much LR
vs. base rock you start out with. Usually in a matter of 2-3 months you should start to see some visible growth and within 6 months to a year it could be fully transformed.
It will not happen overnight and you have to be patient as with everything else in this hobby.
This is what I did starting out as I did not want to pay the price for LR
, especially when much of it is covered with other rock. If you are patient it can work out very nice and be very cost effective.