Depending what operations you need to perform, you may be able to keep your data as a datetime array without converting it to serial date numbers. But if you do, datetime can convert serial date numbers into a datetime array.
>> dt = datetime('now')
>> sdn = datenum(dt)
>> dt2 = datetime(sdn, 'ConvertFrom', 'datenum')
As an example of some operations defined on datetime arrays, you can perform date and time arithmetic using datetime and duration arrays.
>> dt3 = dt + hours(1) + minutes(2) + seconds(3)
>> du = dt3 - dt2