Good luck, cant remember how long it was inbetween duvet stains and birth it was quite a few litters ago, vaguely think it was about 24 hours. Just watch her for any signs of struggling, i.e. pushing for hours and hours and nothing happening, anything nasty coming out. Signs of starting... the queen panting (yes mine do that gob open and all that), or if the first kit is on its way out you will see a plastic looking sac, like a condom pmsl, this is the babe's head normally. The sac over the head has to come off within a few minutes or the kit will suffocate. The queen may do it, or you can split it yourself with fingers to make sure the kit can breathe and open its airways with your little finger (common sense, making sure you have washed your own hands with antibac
).
You'll probably find the queen will do all this as course of nature, but watch her like a hawk as they dont all behave as per mother nature's rule book
