depends on whether it was made by some fancy upscale luthiers or by $1 per hour chinese factoryworkers (in which case it might never even be able to be in tune)
I think you mean ''How long does a new guitar stay in tune''

And it depends when the strings were put on.
.Brand New.Bright Eyes.This Will Destroy You.

What kind of bridge it is helps alot.

EDIT: Your RG320 is kinda the low end and will probably cause alot of problems unfortuneately.