One week shouldn't hurt, but...If you can put them under 20/4 right off the bat, I would go that route instead. Each week for autos is a big deal. If we only have 3-5 weeks of veg, it's best to give them the utmost optimal conditions in this time so our end-game yield won't be affected. If I slow my photo-periods down, no issue. I can just veg for longer to get to where I want to be. If you slow your auto for too long, there's no turning back or extra time to veg. It will be what it will be and flower as such, probably with a low yield (bud may be just perfect but there won't be much of it).
Suggested to leave them be and plant them when you have the ability to throw them under a straight 20/4 cycle. I know that's not ideal and you're trying to save some time, but in another week you can be confident you won't be hurting your end game product/yield.
Give me a shot in PM if you think there's anything else I can help you with. Cheers and good luck!