About 2-5 yr if ever
Handedness is prewired into the system and may emerge in the mid 2nd yr or later if ever. Some kids will use one hand for one action & the other for another. A few will be ambidexterous for a lifetime.
There is never a reason to push a child to use or not use a given hand, you won't change it. Preferance for one hand before 15 mo may be a sign of neurologic problems
& deserves an evaluation.