Hi Witchy - I think Tang runs his auto perpetually.
You can stagger them 2-3-4 weeks apart for constant harvesting. It's not for everyone (as personally i don't relish the thought of having to harvest every couple of weeks)
BUt can certainly be done - especially if you have a strain dialled in and are running them constantly.
With different strains, just do your homework to make sure they're not a long flowerer (which will mess up your rotations)
Hope this helps
Blue ^_^