How to add a date/time with a real number (decimal hours) to create a new date/time

I have a column with start date in date /time format and I would like to add a cum duration (decimal hour) to that start date to know the exact date/time (hh:mm) of a particular task.  The source of my data doesn't provide me with that.  I think if I somehow convert the real number representing decimal hour to a time format hh:mm then it would shorten my steps.  So far I've used the expressions and three intermediate calculated columns:  

DateAdd("hour",[Cum Duration],[dttmstart])    `adds the hour

right(String([Cum Duration]),3)     `converts to string and captures everything after decimal 

Cast ([Minutes] as Real) * 60 `converts to real minutes 

DateAdd("minute",[Minutes (Real)],[task time (hour)])    'Adds minutes to the previously added hour task time column

This seems like a lot of steps to accomplish what I am doing.  Any shortcuts appreciated.



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