In the winter the Morzine lifts usually start to open from the second week of December onwards. Normally only a few lifts are open for the first week, with progressively more lifts opening as snow permits. You may find that the higher resorts of the Portes du Soleil have the most lifts open towards the start and end of the season, as they have more dependable snow coverage than those resorts lower down.
Getting up the first and last lifts of the season can sometimes means you won't experience the best snow ever, but you may find that you have the pistes to yourself, no lift queues and sometimes there are low-season discounts to be had. Spring skiing can be pleasant with warmer weather and more precipitation can mean more snow! The season usually ends towards the end of April.