To compute datetime ID values from calendar and time variables, first compute the date and then compute the datetime with DHMS.

For example, suppose you read tri-hourly temperature data with time recorded as YEAR, MONTH, DAY, and HOUR. The following statements show how to compute the ID variable DATETIME:

data weather;
   input year month day hour temp;
   datetime = dhms( mdy( month, day, year ), hour, 0, 0 );
   format datetime datetime10.;
datalines;
91 10 16 21  61
91 10 17  0  56
91 10 17  3  53

   ... more lines ...