Wow 17 weeks is a LONG TIME!

The veg period is up to you. If growing from seeds, it can take 6-8 weeks to show sex. However clones are cut from a mature plant and can be flowered as soon as they have roots.

Once you go into flower (12/12) it takes anywhere from 8-12 weeks to mature the buds. Nutes will help grow bigger buds, as will CO2. However the time it takes to mature is still 8-12 weeks.

Pure Indicas mature in 8 weeks(ish)

Pure Sativas mature in 12 weeks (ish)

ANY cross (depending on percentage of indica/sativa) can be anywhere in the middle.

At 15 weeks of veg, these must be HUGE!