String DateTime Formatters em C#

SpecifierTypeExample (Passed System.DateTime.Now)
dShort date10/12/2002
DLong dateDecember 10, 2002
tShort time10:11 PM
TLong time10:11:29 PM
fFull date &time
December 10, 2002 10:11 PMFFull date &
time (long)December 10, 2002 10:11:29 PMg
Default date &time10/12/2002 10:11 PM
GDefault date &time (long)
10/12/2002 10:11:29 PMMMonth day pattern
December 10rRFC1123 date string
Tue, 10 Dec 2002 22:11:29 GMTsSortable date string
2002-12-10T22:11:29uUniversal sortable, local time
2002-12-10 22:13:50ZUUniversal sortable, GMT
December 11, 2002 3:13:50 AMYYear month pattern
December, 2002
Custom date formatting:

SpecifierTypeExampleExample Output
ddDay{0:dd}10
dddDay name{0:ddd}Tue
ddddFull day name{0:dddd}Tuesday
f, ff, …Second fractions{0:fff}932
gg, …Era{0:gg}A.D.
hh2 digit hour{0:hh}10
HH2 digit hour, 24hr format{0:HH}22
mmMinute 00-59{0:mm}38
MMMonth 01-12{0:MM}12
MMMMonth abbreviation{0:MMM}Dec
MMMMFull month name{0:MMMM}December
ssSeconds 00-59{0:ss}46
ttAM or PM{0:tt}PM
yyYear, 2 digits{0:yy}02
yyyyYear{0:yyyy}2002
zzTimezone offset, 2 digits{0:zz}-05
zzzFull timezone offset{0:zzz}-05:00
:Separator{0:hh:mm:ss}10:43:20
/Separator{0:dd/MM/yyyy}10/12/2002
Fonte: http://blog.stevex.net/index.php/string-formatting-in-csharp/