I think the key is usage. How many are in the family? What are the "bathroom" habits?
If it is just a couple then you should be OK with waiting until the 2nd weekend - just be sure and dump plenty of water into the holding tank before letting it sit. If there are a lot of you then you might not be able to wait that long. If you intend to put it away for a week or longer in hot weather you might want to dump it to avoid any smells that might accummulate as the black tank "percolates"
