Meditation can definitely cause you to sleep less. When meditating one is naturally entering a calmer state of mind.
When doing Samatha meditation one is temporarily suspending the hindrances thereby limiting the effect of worries, excessive thinking, restlessness, cravings, aversions, anger etc. This naturally leads to a more simple and unified mind. Such a mind will affect the physical body and calm it down.
The human brain uses more energy than both arms and legs together on e.g. cognitive processes. All the stress from the hindrances will sooner or later manifest itself in the physical body as stress, i.e. an increased secretion of stress hormones such as cortisol and adrenalin. This will create a lot extra tension and load on the internal organs which in turn will increase the demand for energy.
The result of that is the need for more sleep.
Now if one removes the above things then one naturally needs less sleep.
If we take a look at Vipassana Meditation then here we are directly working with the hindrances, i.e. by weakening them to the point where they can be eradicated completely. In vipassana meditation we learn to see reality for what it is, meaning that the mind do not extrapolate on phenomena. The mind do no follow after phenomena thereby launching a process of ideation and planning on how to posess the object.
A non-meditator, i.e. the untrained mind will not have this ability to see clearly. The untrained mind will see an object for a brief moment whereafter it will launch the process of ideation, extrapolation, judging, imagining, liking, disliking etc. Imagine how much energy these cognitive processes demand.
If one trains in clear comprehension one gradually builds the ability to stop the mind from launching these cognitive processes by applying mindfulness to mental and physical phenomena as they arise and cease. With time and training the mind will become deeply rooted in the present. It will become calm, peaceful and equanimous no matter what arises.
A reduction in mental stress levels results in the physiological processes of secretion of stress hormones will be stopped and reversed resulting in a calmer body and a lot less load on internal organs.
At night the body regrows tissue, builds muscle and bone and strengthens the immune system. When there is less load on the body then it also needs less time for restitution, i.e. less time to sleep.