If it says 60 days, it's more like 80. If it says 90 days it's probably closer to 120. Sellers usually lowball their flowering time to entice growers into buying them thinking they going to get a faster harvest. But as Herb & Suds said, start counting when you see the first pistols forming. Usually around two weeks after flip to 12/12.
You can look at user reviews on the seed sites or put the strain name in a search on a forum to find out true flower times (well, within a week or so). Or just post the strain and ask about it if you can't find much.
If using forum/google searches you need to use the exact name and only take info from a strain topic with the exact name. A lot of strains sound similar or people forget to mention or add on bits like ''kush''. It makes a difference if you need the info for heights and various other attributes.
Ready to harvest or wait 1 more week? I think 1 more week, the night temps dipping to the 50s last week or so and I think it slowed maturation but all next week upper 70s and low 60s at night. Any thoughts are welcomed.