If one divides Screen Time by Screen Percentage, one gets Active Time. I've noticed Active Time stays pretty constant while my Screen Time varies a lot with s5 use. I keep my s5 in Ultra Power Saving Mode when not in use.
My Screen Time has varied over 11 cycles from 0:34 to 5:40. My Active Time has ranged between 17:09 and 22:40. I've charged at levels ranging from 12% to 23%. I've gotten from 4 to 12 days until a charge was required. I track it all in an Excel Spreadsheet.