All of a sudden, cannot set appointments on the quarter hour! I must be able to! How to fix this?

Having the same issue and it is a big problem. I've gone into the time drop down area and manually entered :15 or :45 but it reverts back to :00 or :30. 

Exactly.  Zoom needs to fix this, but there is no way to directly communicate with them with the Pro version. 

I may have answered already, though don't see my answer - You can type in any time you want but you must also type in AM or PM. Without that, it does revert to an on-the-hour or on-the-half -hour time. The old way had the AM/PM as a drop-down also.  Now it does not, so type it in with the time you want and it will not revert back. 

I've tried this and still cannot get it to work. 

OK...I figured it out.  You have to type in the time you want manually with a space between the time and the AM or PM that must also type in, since the quarter hours are no longer in the drop-down menu.  Then, while what you typed is still in the window, you will see the time you typed in show up just below where you typed.  You need to click on that - the same time just below the box in which you type -  and it will then do what you want, keeping the reservation for the time you want. Then when you go over to the ending time, the ending choices will be in quarter hours - but not on the hour or the half hour. The end time doesn't matter as much, but it is annoying that they made this change. 

For whatever reason, as I manually typed in today (Edit a meeting I set up yesterday), it showed in the drop down box. Not yesterday, but it did today. I clicked on it and all good.