set

The command to reset the system time to 18-APR-2010 09:47 is:

$ SET TIME=18-APR-2010:09:47

Note the colon between the date and the time specification. (This
extra colon is a requirement resulting from the DCL parsing rules.
Normally, there is a space between the date and time.)

—

On OpenVMS VAX, once a year between January 1st and circa April 11th,
or whenever a different SYS.EXE system image is bootstrapped, issue the
command:

$ SET TIME

to resynchronize the VAX time-of-year (TOY) clock and the contents of
the OpenVMS VAX system image. (This SET TIME command is automatically
performed during a normal system shutdown.) The TOY clock stores (only)
the time since January 1 00:00:00.00 of the current year, and has a
maximum resolution of roughly 466 days. The system image is used as the
storage location for the current year. Between these two values, the
current time and date is “constructed” during the OpenVMS VAX system
bootstrap. (And this is the reason the saved time value in the system
image must be reset every year between January and April.)

—

The SYSGEN parameter SETTIME can be used to enable prompting for the
system time during the system bootstrap.