I finally got it. At 0900 in the morning! I don't know what's up with that. It's probably best that scene can unlock at anytime during daylight hours.There is no bug or anything wrong with the 2nd Yvette bikini scene. Matter of "luck/random". It took me some times to unlock it either. Try at different time between 11h and 17h and not always at the same time.
There was also nothing wrong with the sauna scene.
Also, the sauna scenes worked perfectly fine. The issue was catching Yvette in the damned thing for only 2 days in the week lol. So yeah there was nothing wrong with the coding or anything but by design and the sheer randomness of it all progress came to a halt for me until I could thankfully force code her into the sauna and go on about my 500th or whatever game day. I don't mind a little grinding but damn!
Anyways, thanks for the quick reply.