I have done it a little over 24hours after but I obviously prefer to let it cure fully. A lot depends on the concrete used, conditions, and the customer or homeowner.
I usually build the frame for it out of 2x10s and if it is a must get the system up and running that day I run a few boards across the top of the box, just above the concrete and install it hovering an inch above, come out a few days later and move and secure everything. Not ideal but when given the choice of a pad thats agonna be bad or having some ugly lumber in the homeowners yard for a couple of days I like to walk away from the job knowing I don't have to worry about it failing.
If you can possibly wait for the pad to fully or mostly cure before you go slapping the condenser on there that is what I would do.
How many days are we talking about? 2? 7? I think my installer was talking about that setup of having it hovering over the pad. I just didn't confirm with him that he would come out 3 times just to allow me to install the pad.