You can vege for as long as you want before flowering.

Many say 3-4 weeks because they are growing SOG style with 10-200 plants and need the plants to maintain an even canopy.

If your growing just a single plant for personal use, I'd vege a month and a half from clone, possibly 3 from seed.

As for cutting a clone, if it's from seed make sure you've got it sexed first. No reason to clone a male unless your breeding

Got any pics of your proposed "mother"?