The internal representation uses two variables to define the date and time of an event. One variable (integer*2) is the number of days since 1-Jan-79 (DS79) and the other (integer*4) is the number of milliseconds from the start of the day to the event (MSOD). Almost all data are saved using this internal representation which uses a total of 6 bytes.
The Yohkoh structures use the internal time representation and store the two values in tags .TIME and .DAY. The routine GT_TIME and GT_DAY will extract the data in these fields (the routines are needed because the .TIME and .DAY fields are nested in the .GEN portion of the index structures).