function GetDateTimeString(const DateTimeFormat: String; const DateSeparator, TimeSeparator: Char): String;

Returns the current date and time as a string using the specified formatting. The following format specifiers are supported:

d Displays the day as a number without a leading zero (1-31).
dd Displays the day as a number with a leading zero (01-31).
ddd Displays the day as an abbreviation (Sun-Sat).
dddd Displays the day as a full name (Sunday-Saturday).
ddddd Displays the date using the system's short date format.
dddddd Displays the date using the system's long date format.
m Displays the month as a number without a leading zero (1-12).
If the m specifier immediately follows an h or hh specifier, the minute rather than the month is displayed.
mm Displays the month as a number with a leading zero (01-12).
If the mm specifier immediately follows an h or hh specifier, the minute rather than the month is displayed.
mmm Displays the month as an abbreviation (Jan-Dec).
mmmm Displays the month as a full name (January-December).
yy Displays the year as a two-digit number (00-99).
yyyy Displays the year as a four-digit number (0000-9999).
h Displays the hour without a leading zero (0-23).
hh Displays the hour with a leading zero (00-23).
n Displays the minute without a leading zero (0-59).
nn Displays the minute with a leading zero (00-59).
s Displays the second without a leading zero (0-59).
ss Displays the second with a leading zero (00-59).
t Displays the time using the system's short time format.
tt Displays the time using the system's long time format.
am/pm Uses the 12-hour clock for the preceding h or hh specifier.
Displays 'am' for any hour before noon, and 'pm' for any hour after noon.
The am/pm specifier can use lower, upper, or mixed case, and the result is displayed accordingly.
a/p Uses the 12-hour clock for the preceding h or hh specifier.
Displays 'a' for any hour before noon, and 'p' for any hour after noon.
The a/p specifier can use lower, upper, or mixed case, and the result is displayed accordingly.
/ Displays the date separator character given by the DateSeparator parameter.
If DateSeparator is set to #0, the system's date separator character will be used instead.
: Displays the time separator character given by the TimeSeparator parameter.
If TimeSeparator is set to #0, the system's time separator character will be used instead.
'xx'/"xx" Characters enclosed in single or double quotes are displayed as-is, and do not affect formatting.

Format specifiers may be written in upper case as well as in lower case letters--both produce the same result.

GetDateTimeString('ddddd', #0, #0);
GetDateTimeString('ddddd tt', #0, #0);
GetDateTimeString('dd/mm/yyyy hh:nn:ss', '-', ':');