Like Miloboy said, it depends on the boy for the most part. Takes a bit of work on your side too, if your partner hasn't got a larger knot you'll need to clench a bit to prevent your sphincter from slowly dilating, you'd be surprised how wide you can open up when something large is tugging at your ring from the inside hehe. If you've been doing your kegals like a good boy and your partner is a seasoned bitch breeder you could be in for good 3/4 hour filling