There are some autos that claim to finish in as fast as 6 weeks - don't think I've seen a 5-weeker.

If they finish in 6, they'll usually be dwarf-sized with smallish to mid-range yields - you certainly can't expect a branch-breaker in those timeframes.

I think you'd be happier with an 8-10 week finishing Auto - and you can certainly find dwarf-sized strains in that timeframe.

Northern Lights is on the smallish size & has a fast finish - but that's the finish & doesn't include the veg stage which will vary by person.
That being said, some people will use seeds that stretch during the finish & put them straight into the flowering stage to reduce the time - someone else would have to say, but I don't think that's such a good idea with Northern Lights - I don't think it has the stretch.

Lots of ways to go about it, but I don't think 5 weeks total from seed is going to happen.

You can find all our Autoflowering Seeds by clicking this link.
That's our international site. If you're in the UK, I can give you a similar link with a wider selection.