I let my welsummer sit for for 5 days after I got them so they would go into the bator at the same time with silkie eggs. I didn't want a staggered hatch so had to wait for silkies to arrive first. I set 12 welsummer eggs and so far 9 look great and 3 I can't tell they are to dark to see in. But it's up to you most people only let them set for 24 hours.