Supercell, this is more than fair!
A 24h cool down will be frustrating as every time you change a gb location after someone attacks and points out the weakness, you cant challenge for 24h cz of it. Will just cause more frustration and less excitement for the update. Rather, what i propose is, keep a 10s timer EVERYTIME you click on layout editer. So you can do a minute change, leave and still challenge. It's not humanly possible for someone tomake a base in 10s.
ALSO, If you leave your layout unfinished then the 24h cool down applies so you dont try doing a little change every 10s and make a base. Fair enough?