Aram, Excel's notion of time is more or less equivalent to a datenum in MATLAB (with a different offset). In other words, a count of days + fractional days, either from an implied offset of "0"-Jan-1900 (if you are talking about an absolute time), or just the raw count (if you are talking about elapsed time). I don't know all the details of Excel's internals, but my impression is that to distinguish absolute from elapsed time, you change the display format.
A calendarDuration is a much subtler thing, in effect a 3-tuple comprising a count of months, days, and seconds, and in general it's not possible to turn that into a single number (how many days in a month? it depends. How many seconds in a day? it depends). In that sense, a calendarDuration is more like a datevec, not a datenum. It may be that you've called caldiff to get just the number of days, and for special cases like that you can certainly write out something (probably you'd convert to numeric using the days function).
I think you'll need to say more.
