Well, if there has been no die off from the rock (they stayed wet during transfer) and depending on the sand it could be very soon. Although, the beneficial bacteria will be limited as it's essentially just the live rock for now. Test for ammonia, nitrites and nitrates, if the numbers are 0's then you could add a small dose of pure ammonia to ensure that the system can handle it and test the next day. If it's 0's, you could slowly add the fish, watching the parameters and ready to act if the numbers get too high.