New Marine Setup - Live rock questions

I have currently got a new marine tank setup going and its in the
first few days of infancy.

I have a RIO 125 tank with a Fluval 204 external filter, marine-glo
and aqua-glo lighting. There is about 1" of crushed coral sand as
substrate too

I would like advice on when or if to put live rock into the tank and
whether or not to use it to aid the cycle of the tank.

If live rock is a good idea how soon should I put it into the tank and
how much should I get?

Thanks in advance

Neil