The short answer
Usually somewhere between 20 minutes and an hour and a half each way, depending on how far into Erg Chebbi your camp sits. Camps close to the dune edge are a short ride; camps deeper in the sand take longer. You ride out in the late afternoon to arrive before sunset and ride back after sunrise.
In more detail
The ride starts at the edge of the dunes near Merzouga village, where your driver leaves the car. Our guides give a range rather than one figure because camps differ: some sit a short ride from the road, others are set well into the erg. If the time matters to you, ask the camp before you book.
The ride is timed for the light. You set off as the sun drops so the sand changes colour around you, and you reach camp in time to climb a dune for sunset. The next morning you are woken early to watch the sun come up over the crests, then ride back for breakfast or after it.
A camel guide walks in front on foot, leading the string. The pace is a slow walk. If you would rather not ride, most camps at Erg Chebbi can bring you in by 4x4 in a few minutes, which suits young children, bad backs and early departures.