24 hr time calculations without semi colons

It's a long time since I have used excel and I have after a long illness just got back to an old project. Unfortunately, I have forgotten a lot that I had previously learnt from this forum despite re-reading my previous posts
I have attached a sample created in excel 2010.
Row 5 with times entered with the semi colons works just as needed and the calculations in H,J,K,L work OK.
but the full workbook will need lots of entries so I want to do away with having to put in the time consuming semi colons.
In row 6,I have entered the times without the semi colons and formatted the cells as 00\:00.
What my question is, Does anyone know how can I get columns H J K L to do the calculations? in row 6
Thank You