Is it allowed to extend or shorten the stay during our meeting?

You can leave any time earlier if you want. But keep in mind that there won't be any refund in that case. In other words, if you book me initially longer and then decide to leave earlier, you will have to pay the amount for what you booked initially, regarding how early you leave.

You can extend your time based on my availability and possibility. The extra hours will be calculated based on the spontaneous booking price ("same-day rate") for that particular day. So, for instance, if you booked me initially for 3 hours with the advance booking rate 100 Euro per hour, and you decide to extend the booking by 1 hour, then the extra hour, according to my pricing, will be with the "same-day rate" 140 Euro extra if that booking is made during the weekdays (Mo-Fr, according to the current pricing).