How long before villagers can breed again?

About five minutes. After a baby pops out both parents go on a cooldown of roughly five minutes before they'll do it again, and they need to be willing again too, which means enough food in their inventory, bread, carrots, potatoes or beetroot, and a spare bed within reach for the new one. If they're not breeding at all it's nearly always beds, there have to be more beds than villagers, and the beds need two blocks of air above them.