I do rooting in a homemade abb and flow/nft hybrid set-up
15 minutes on and 1:45 off. watch your hydroton to see if it get's too dry before water cycle. if so, then shorten off time until your medium is almost dry. hope this helps.

p.s. commercial lettuce growers use ebb and flow to root there veggies before placing same in nft or drip for vegging.