Productivity Formula Help

Hello Experts,

I have changed my productivity spreadsheet to include start and finish times and now I can't work out the productivity correctly. Before we were manually typing in 2.5 if it took 2 and a half hours and now the time formula it says 2 hours 30 minutes.

For example:

6000 units scanned / 5 team / 2.5 hours to complete = 480 units per team member per hour

Now in the new template that automatically works out the hours and minutes based on the start and finish times

6000 units scanned / 5 team / Took 2 hours 30 minutes to complete = 11520 units per team member per hour which is very wrong.

I just need help with if I need to change the formula or change the formatting of the cells as we keep track of stocktake productivity for 150 stores.

Thanks so much!