Delta time implies 2 times--a starting time and a terminal time. Does your Time class represent a single time or an interval between 2 times? Where does the second time come from?
Assuming that Time represents a single instant (e.g. Jan 31, 2018, 8:32:16 am) and not a time span (1/31/18 08:32:16 through 2/23/18 04:00:00), I would add a function that returns the delta between the starting time represented by the Time object and a Time argument representing the terminal time. You would have to determine in what units to return the delta. You might want to call this type Interval. (Interval could be number of seconds, a struct containing years/days/hours/mins/seconds, or something else, depending on what you need).