Most desert tours from Marrakech or Fes sell a one-night "quick" Sahara add-on, but it means a grueling 8-9 hour drive each way squeezed around a single camel ride and one night in camp — you'll spend more time in the vehicle than in the dunes.
A two-night itinerary breaks the drive up with stops at the Todra Gorge, Ait Ben Haddou kasbah, or the Dades Valley, and gives you a full free day at Merzouga or Zagoura to actually explore the erg on foot, by camel, or by sandboard, plus a proper sunrise over the dunes on the second morning rather than a rushed one.
If your schedule truly only allows one night, it's still worth doing — just go in with the right expectations about how much of it is driving.
