Something seems off. The single blade leafs almost look like its re-vegging or just one of those 'newer unstable strains as mentioned above.
Anyhow, people calculate "flowering" weeks a few different ways. From light switch, to actual flower formation, from end of stretch. In the end, most go by trich color so it's kind of irrelevant. Just gives a ballpark idea of where you're at. From the looks of your pistols, you've still got weeks to go my friend. I'd go as far as saying 4-5wks since your pistols are still white. Keep doing what you're doing. All looks good, should fatten up a ton!