There's only one reason I see that the value in cell F87 is wrong; it not summing the right range. The formula is currently:
=SUM(F85:F86)
A better formula would be:
=SUM(F54:F84)
which gives 4 hours, 50 minutes and 4 seconds
If there's a possibility that the time summed exceeds 24 hours you'd be better formatting that cell with custom format:
[h]:mm:ss
with the square brackets enabling the display of hour values greater than 24.


If you select the single cell where you want the sum to appear, away from other cells containing data, then click the sum symbol, you'll get just
=SUM(|)
in the cell with the cursor sitting within the parentheses, do nothing except select the cells you want summing and press Enter on the keyboard.
The only difference from what you were doing is now you're selecting (highlighting) the cells you want to sum after clicking the sum symbol rather than before clicking it.