Thyme is an evergreen plant so persists through the year rather than "returning". But it prefers full sun, excellent drainage and dislikes summer humidity......that could be a limiting factor in your location.

Thyme is commonly planted in between flagstones. In my area it is usually sold in 4" pots that can be sliced in half or in quarters to fit in between the stones. Sometimes you can purchase it in smaller 'plugs' that make dividing larger pots unnecessary. Just plant in open areas between the stones. Might need some water the first season to become established but not too much. After establishment, it should be able to survive on just rain water.

Be sure you get a form of creeping thyme (and there are LOTS!). Culinary thyme, Thymus vulgaris, is too tall and upright and woody to make a good groundcover.