I am new and don't have a tank yet. But from what I read if you are doing a fishless cycle then no water change is needed until cycle is finished. The theory is that doing a water change now might increase the time to cycle the tank, someone else will have to confirm.
do your water change AFTER your ammonia and nitrites are at 0 and u have readings of nitrates....the water change will bring your nitrates down and help balance your ph out...your cycle shouldnt take that long with lr and ls
If the ammonia/nitrite get to high you may want to do a 25-50% water change to save the life on the LR. It may prolonge the cycle but it causes less shock to the micro/macro fauna on the LR and LS. HTH