well it takes 3 days for a egg to hatch, drop it in and check it in the morning and evenings, when you see eggs then you know when it will hatch, ain't hard, look on the side or middle of the hive and look for eggs or young brood and place it there, it could happen the first day and then again they might want to polish the cells a day or so before she lays, easiest way is look for young larva and graft from those ;) , easier than you think!