INT 21,2D - Set Time

AH = 2D

CH = hour (0-23)

CL = minutes (0-59)

DH = seconds (0-59)

DL = hundredths (0-99)

on return:

AL = 00 if time change successful

= FF if time invalid

- changes DOS maintained clock

- DOS version 3.3+ also update CMOS clock where applicable