Change Duration Unit

Hi I just installed your plugin and I love it- great work!
The only thing I had the same problem as here http://ww.wp.xz.cn/support/topic/plugin-appointment-calendar-booking-timesservice-duration?replies=9
But fixed it with a small fix.

But I can’t find an option to add or just change Duration Unit types – I need it to be Hours instead of Minutes. While creating a new Services you have a drop-down menu for Duration Units, so there should be way to have different options there, or not?
Please advice me how to fix it or where to find it.

Thanks.

http://ww.wp.xz.cn/extend/plugins/appointment-calendar/