I use Beersmith to brew with, it tells you the expected SG when primary is completed. I have been going by the readings and I get a varying amount of days with each batch, some lasting as short as 3 days and up to 10 days on some. The beer is turning out great. I read alot where people are in primary for 2 weeks or longer as a standard practice for all their beers. Should you go by SG readings or a set time?