The short answer
You can, but we would not. Chefchaouen is about 200 km from Fes, roughly 3h30 each way by road, so a day trip means seven hours in the car for a few hours in town. You would miss the quiet evenings and soft morning light that make it special. Stay at least one night, and ideally two.
In more detail
The road runs through the Rif's olive terraces and cork-oak forest via the holy town of Ouezzane, and it is a fine drive. Doing it twice in one day is the problem. By the time you arrive, the medina is at its busiest with other day visitors, and you leave before the light turns gold.
A better plan for northern Morocco: four nights in Fes, then two nights in Chefchaouen, then either back to Fes or on to Tangier, about two hours north. CTM buses run Fes to Chefchaouen, and a private driver makes the trip easier with luggage.
If Chefchaouen is the main reason you are going north, it is also possible to fly into Tangier, visit Chefchaouen first and continue to Fes, so the town sits naturally on the route instead of being a detour.
Good to know
- There is no train to Chefchaouen.
- Arrive in the afternoon and walk up to the Spanish Mosque for sunset.
- Book the upper medina for quieter nights.