DateTime  is a monotonically increasing  floating point number which represents any PointInTime.

It is made by combining two integers with a  period between them:  
DateStamp'''.'''TimeStamp 
-- some locales may use the comma ''',''' instead of the period'''.'''

'''YyyyMmDd.HhMmSs'''
I saved this wiki page on 20110811.16260907 and then again 20110812.22294007

Meetings have dates '''and''' times.

Many date and time operations are simply trying to tell which of two came first, 
or if this date and time falls within that interval or not.

Simple numeric comparisons, no parsing.
 Which came first:  simple comparison Before < After ?
 Within interval:  Before < Is it here? < After

Computing differences is more complicated, but that's what we have computers for.  

''Exempli gratia'': How many days have I been alive since 19540216.08330005?

or 
"If the flight starts in San Diego at 6:15am and 
flight time is 27 hours and 38 minutes, 
What time will it be when we arrive in LuleåSweden?"

 If you are serious
Answers -> ItDepends on many things - some of which:
* to First Question
** What time is it now in the same FrameOfReference?
** What time is it now in the place the origin TimeDate was stamped?
** On what algorithm you use if computing
** On the time to be used as "Now"
** whether you mean complete 24 hour days, or include as a day the current partial day
** use for current day the local day or count Chronological days ( taking into account the international date line )
* to Second Question
** If the answer you want is about what time it is LuleåSweden or San Diego - your FrameOfReference
*** WristwatchTime 
*** LocalTime 
*** SmartPhoneTime
** On successful arrival at LuleåSweden, rather than SomeWhereElse  
*** What the actual flight time is
** If not arriving at LuleåSweden
*** What you do about being in a DifferentPlace
 if not serious
Who cares? - you don't really want to know, see StrawMan, StakeInTheGround, ConversationalChaff, EmpiricalEvidence