daphnia ephippia - freeze how long?

Greetings! I've searched the net for info on how to get daphnia ephippia to
terminate diapause. My small daphnia culture crashed last year, leaving
behind about 60 ephippia. I've seen reports that they'll hatch if I just
add water. I've seen other reports that suggest they need several
freeze/thaw cycles. I'm trying both methods, but nowhere did I see how long
to let the freeze/thaw batch stay frozen. Are we talking a few hours, a few
days, a few weeks, or do I have to simulate an entire winter? How long
between cycles? Do I leave them thawed for a few hours, a few days, etc?
What is more important, the fact that they get frozen at all, or the length
of time they spend frozen? Thanks for any advice!
ml