Both wet & electric operate using different zones for each area of the house. Wet use a combination of manifold & thermostats. Electric will just use thermostats.
Most thermostats are intelligent now so they work out the timings for power to applied to the heating so all you have to do is set the temp that you want and when you want it.
There is heating up / cooling down times assoicated with wet & electric systems installed in a screed but this is not a issue if you want the system to act as primary heat. The principle of this heating is that you set a comfort temperature for when you want heat and a set-back temp for all other times. This is so the thermal mass of the screed is never lowered too much.
We use an electric in-screed system in our 80m2 office, typically the floor will be charged for between 3-7 hours during the night and this provides was with heat for the entire working day. Obviously this charge is on cheap rate electric and thus is very economical.
Peter