|   |   |            |   |          |
|---+---+------------+---+----------|
|   |   |            |   |  8:00:00 |
|   |   |            |   |  7:55:00 |
|   |   |            |   |  9:00:00 |
|   |   |            |   | 13:00:00 |
|   |   | -8@ 0' 0." |   |          |


#+TBLFM:@>$3=vcount(@2..@-1) * (@>$5-8@)