Format y = Year last 2 digits yy = Year last 2 digits yyyy = Year as 4 digits m = Month number no-leading 0 mm = Month number as 2 digits mmm = Month using ShortDayNames (Jan) mmmm = Month using LongDayNames (January) d = Day number no-leading 0 dd = Day number as 2 digits ddd = Day using ShortDayNames (Sun) dddd = Day using LongDayNames  (Sunday) ddddd = Day in ShortDateFormat dddddd = Day in LongDateFormat c = Use ShortDateFormat + LongTimeFormat h = Hour number no-leading 0 hh = Hour number as 2 digits n = Minute number no-leading 0 nn = Minute number as 2 digits s = Second number no-leading 0 ss = Second number as 2 digits z = Milli-sec number no-leading 0s zzz = Milli-sec number as 3 digits t = Use ShortTimeFormat tt = Use LongTimeFormat am/pm = Use after h : gives 12 hours + am/pm a/p = Use after h : gives 12 hours + a/p ampm = As a/p but TimeAMString,TimePMString / = Substituted by DateSeparator value : = Substituted by TimeSeparator value
Example:

h:m:s.z = 1:2:3.4
hh:mm:ss.zzz = 01:02:03.004
t = 01:02
tt = 01:02:03
c = 09/02/2000 01:02:03
dd/mm/yy hh:mm:ss = 09/02/49 01:02:03
mmm = Feb
mmmm = February
ddd = Tue
dddd = Tuesday
ddddd = 09/02/2049
dddddd = 09 February 2049
hhampm = 01AM
t = 01:02
tt = 01:02:03
dd/mm/yyyy = 09/02/2049
tt, dddd dd. mmmm yyyy = 01:02:03, Tuesday 24. February 2049