I was south of Agadir in July and had mist, clouds sometimes to to Fask (east of Guelmim and wind at night. Saw no snakes only some sheds. There are lots of lizards though, the habitat looks healthy and lots of rodends arround. I was told there is better chance of sun at the coast in all months exept August and sometimes July. This is because of the difference of temperature from the ocean and the interior of Morocco being the greattest. With a bit of sun and no wind (day or night) you must be able to see some nice specimens.
From Marrakech to Agadir you can take the motorway. Do not speed up there are lots of speed control patrols in Morocco, but in 3 hours you have the trip done.
I skiped Agadir and went straight to Massa. Tiznit is a bit further but also a good option, both have good habitats arround.