Sweet potatoes from slips in pots

When do you usually start planting your sweet potatoes? I’m in zone 7b and curious how others time it.

By the way, I came across what’s probably the most detailed YouTube guide I’ve seen on growing sweet potatoes. It shows the whole process step by step with some really useful tips. Thought it might help others here too:  

I glanced at the video, and I imagine it works fine although much of it is unnecessary. I just put mine in trays of damp sand and put them outside in the sun, and cover with plastic if a cold snap threatens, or in an unheated cold frame. I do that about mid-May and generally mid-June or maybe a bit sooner I snap off the slips trim off extra roots and stick them in the ground. Sweet potatoes slips are not nearly as finicky as seems to be commonly believed.  

I don't know what zone I'm in anymore, I'll just say 6-ish.