This is how you can do it. The idea is to subtract two timestamps - one is the one you got and another one created for the same day but at 0 hours and minutes, so the difference will be the required duration:
Object.Duration = TIMESTAMP (1, 1, 2008, HOURS (Object.Timestamp), MINUTES (Object.Timestamp)) - TIMESTAMP (1, 1, 2008, 0, 0)
where Object.Timestamp is the timestamp obtained after import. The day, month and year can be anything but they have to be the same in both timestamps.