Ability to sum up Duration. It should behave similar to SUM

[Steven_Aung]

Say If I like to sum up all duration of a related rows, there’s no such expression right now.
Example,

SUM([Related Tale][Duration])
Yes, there’s a work around by converting each duration to a decimal number, and then use the SUM expression but it will be nice to have a function to summing up Duration and Time.