Calculations (formulas) between 00:00xx and hour columns (3hrs, 2.5hrs etc)

Hi all!
I have a question about formulas, I want to calculate the time a task SHOULD take to calculate the expected end time. I have included a snap shot, but if I were to start a task at 1:00am and it takes half hour, I should finish that task at 1:30. I know it seems like a slightly redundant process but we are just starting to track how long some tasks take, and how much time someone should aim to spend on said task - its a bit of research thing for us at this stage.

Any input welcome!

@Kerryn

This formula should get you started:

IF({Start Hour}, 
  FORMAT_DATE("1/1/1 " & INT((TIMEVALUE("1/1/1 " &
    {Start Hour}) + {Time task takes}/24) * 24) & 
    ":" & INT(MOD((TIMEVALUE("1/1/1 " & {Start Hour}) +
    {Time task takes}/24) * 24,1) * 60),
  "hh:mm A"),
"")

Jim - The Monday Man
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