Here, we’re using seconds, but you can also round if you prefer. She arrives at 9:15:00 AM and leaves at 4:50:15 PM. Let’s say you’d like to calculate how many hours an employee worked, using her clock-in/clock-out times on her timecard. Subtracting time (calculating elapsed time) To add time, type in =A1+A2, and it’ll return the answer in time format (13:15, or 13 hours and 15 minutes).Type 7:30 into cell A1, and type 5:45 into cell A2.The first task will take 7 hours and 30 minutes, and the second will take 5 hours and 45 minutes. Let’s say you’d like to know how many hours and minutes it’ll take to complete two tasks. Type in :mm so that the data displays in an hour:minute format. First, you’ll format the cells for time calculations.Whether you’re adding up employee timesheets, or doing calculations regarding the use of your team’s time on a project, knowing how to do calculations with time in Excel is something everyone in a business environment should know how to do. Adding and subtracting units of time in Excel can be a useful thing to know how to do.