Auto and lighting question

Ok well I want to order some seeds here next week. I am thinking about getting some autos and to try out . I already had a plant that is on 12/12 at the moment that should be done in 4 or 5 weeks…

I was wondering if it would be oke to start the auto and have it under 12/12 lighting until my plant gets done? Say 2 or 3 weeks at the most then I would switch the light back to 18/6 for the rest of the autos life.

I run my autos 16/8 until flower then go 12/12. @WickedAle grows autos 12/12 their whole life. Both get great results