The bus we took (I think the earliest one) left at 8am and arrived at 12:30pm
Cost: 75 dirhams each way
Book the tickets 1-2 days ahead of time from the bus station (we got ours the day before)
We were told this route gets pretty busy and we actually saw a group of backpackers who wanted to get on the bus but there weren't any tickets left
Get the return tickets as soon as you arrive in Chefchaouen, just in case they sell out again. Get the 3:15pm return bus ticket. Chefchaouen is tiny and honestly you don't need more than 2-3 hours there
When you get to Chefchaouen, it's only about 15-minute walk to get to the main area where all the nice blue houses are. Walk uphill towards Bab El Sor (use Google Maps) and just explore the area around it on foot. That's where all the blue houses are