oh, so …the way Karimoo mentioned did not work for you ?
basicaly you use a converted “all numbers format” dateA. add a bunch of minutes xxx …end with a DateB result in numbers… and only after that…you can convert it back to a readable Date format like : dd/mm/yy.
thats what was done in this Topic : Help : StarTIME +60 = funny Endtime 🤔
or you had another result in mind ?