I do know where to find the said button, I simply had no reason to use it, because the sex was over fast enough(even with a demon sex partner) to not matter. But with how slow the sex scene change with your offspring/relatives is, it appears that it would need to be used after all.The quick sex button is your friend in those situations.
Once you have had your fun and gotten your rocks off once or twice, go to the first tab and click the quick sex button and it will finish the scene for you. The button might be on 'Page 2' of that first tab, so click the arrow on the right side and all the other options should appear.
Two other things that would be good to change(which I love in Broken Dreams Correction Center[https://f95zone.to/threads/broken-dreams-correctional-center-v0-1-3-rahimew.158801/]) is the ability to give birth to children from multiple fathers at once, and the Anal Womb option, allowing you to get pregnant through anal sex(without being a slime). It may be somewhat hard to adjust for the pregnancy test(s), but it certainly would be nice to have that, even if only optionally.