Hi,
I would use timeSpan custom actions and string format. They are on the Ecosystem.
"GetTimeSpaneBetweenDates"
"GetTimeSpanInfo"
and so you simply keep track of a start date and time, a current date and time and the spn between the two to then get time spane info out of it.
I use it for a timer app I created a while ago, it works well.
Bye,
Jean