Hey there Ann!
I'm new to trying slips, but just thought I'd mention that my four potatoes have been in the window since Jan 28th. Two have good roots and just started sprouts last week (1/2" long barely). The other two potatoes have just started to root, no sprouts. These are sweet potatoes from my garden last year, so no chemical sprays on them to retard growth.
We're just about zone 8 near Memphis.

South facing window?

When do you hope to plant out?

Yes, South bay window. I think the slips get planted May1st. I plant them amidst the broccoli for shade till they get going, then the broccoli gets whacked as the slips take on enough to handle the sun.
Have not found much info on slips, but I did find one link that said to cut up any long stems, lay in a shallow dish of water to root, then plant those....
How are you doing yours?

I haven't started yet. As I recall, back when I could buy the slips started locally at the Farmers Co-op, they didn't plant them until late May (so weren't available until mid-May) because soil temperature needed to be pretty warm.

I have a large passive solar porch (south facing, of course) and will set them up there. Right now, I don't have really consistant warmth there.