If you are within good reason to ask for flexibility, and the manager(s) at the store are good, they will more than often support your hours. For example, if you are a student or have a back problem, the good managers will work around your hours and demands.
However, if you have bad managers and/or you're asking for less than 16 hours a week, you'll essentially be forced to comply to any and all scheduling they give you.
Flexibles, deux soir semaines minimum pour un temps partiel.
Un soir et une fin de semaine sur deux pour les temps plein.