They are perennial, though sometimes, if in adverse conditions, they can be short-lived. On a wall, such as the ones in your photo, they are liable to be fried alive in hot weather.
In a trough, for instance, where they can access more moisture at their roots, they are less stressed and so both stay green longer. Many plants here in our Aberdeen garden stay evergreen.
I'd scatter the seeds now in a trough if you have one, or in a raised bed ( it's nice to be able to have these diminutive plants raised up where you can see them more closely) though they'll even be happy in the front of a border. If you want to try them on a wall I'd store them in a paper bag somewhere coolish until the weather cools down a bit before you try "mud-cementing" them on a wall.
I'd establish some plants in an easier spot before I tried to get them on a wall, though. It's very tricky to do that artificially, even though plants like this Erinus and the delightful Cymbalaria muralis "do it themselves" with such apparent abandon!