is there any way to make royal icing hard withing 5 hrs.
Maybe add more meringue powder than usual? It will crust over but still not be dry inside, though. Less water to begin with will help, too.
try putting them in the oven with the temp off but light on for awhile.
They won't be solid dry but they will be better than just air drying.
Don't keep opening the oven though. Get them all in there and then leave it closed until you need them.