shouldnt take that long supect it will take 3-4 months but that isnt any longer than most strains if started from seed the only reason it would take 5-6 months is if you was going to let it grow for 3 months before switching to flowering the plant would get very large but not generally done on indoor grows and certainly not done in cabs.
you might consider reading up on taking clones and keeping mother plants as it is certainly quicker than growing from seed.