The toDateTime(...) function has eight variations, not counting syntax variations. You can convert a String to a DateTime with optional custom format string and optional time zone. You can also convert separate Date and Time values to a DateTime with an optional time zone.  Finally, you can convert an Integer to a DateTime.

Syntax:
toDateTime( datetime-string )
toDateTime( datetime-string, format-string )
toDateTime( datetime-string, format-string, timezone-string )
toDateTime( date, time )
toDateTime( date, time, timezone-string )
toDateTime( millis-since-epoch )
toDateTime( millis-since-epoch, timezone-string )
toDateTime( datetime-value, timezone-string )
datetime-string.toDateTime()
datetime-string.toDateTime( format-string )
datetime-string.toDateTime( format-string, timezone-string )
date.toDateTime( time )
date.toDateTime( time, timezone-string )
millis-since-epoch.toDateTime()
millis-since-epoch.toDateTime( timezone-string )
datetime-value.toDateTime( timezone-string )

 

Parameter	Description
datetime-string	The String value to be converted to a DateTime value.
format-string	The format string is used to interpret the time-string. If omitted the default format is "MM/dd/yyyy h:mma" which is the 2-digit month, a slash, the 2-digit day, a slash, the 4-digit year, a space, the hour, a colon, the minute and finally either "AM" or "PM".  For a description of possible format-string values refer to the Java API documentation for SimpleDateFormat.
timezone-string	The time zone string is used to convert the dateTime value to a Time.  If omitted, the current user's preferred time zone is used.  Any time zone identifier supported by Java 5 is allowed.
date	The Date value to be converted to a DateTime value.
time	The Time value to be converted to a DateTime value.
millis-since-epoch	The Integer value to be converted to a DateTime value.  The number should be the exact number of milliseconds since epoch.  Epoch for Relate Script is Jan 1, 1970 at midnight GMT.
datetime-value	The DateTime value to be converted to another DateTime value at the same moment in time but in a different time zone.