If it is a true auto, it will bloom under 24 hour light - They have their advantages in short season latitudes ...
Some things to consider:
Because they are auto's, they are essentially 'put and take' plants - keeping a mother is near impossible - must pop new seeds each run.
Most I see advertised are 90 to 120 days start to finish.
However, there are many non autos that are ready in 50 days or less of bloom, add 30 days of veg and you still have a plant that is done in under 100 days AND you can keep a mother for future cuts.
Not denigrating auto's, as I said they have advantages in the right clime, but non-autos can produce in the same period with a larger selection of strains available.
Cheers