As you may be aware it is possible to change your password from the command line using the net user command,
and if you combine this with the at command you can run the command on different machines, e.g.
at \\<machine name> <time> cmd /c net user
e.g. at \\savilljohn 18:00 cmd /c net user Administrator password
The /c after cmd causes the command window to close after the command has been executed. An alternative to the at command
would be the soon command
soon \\<machine name> cmd /c net user Administrator
For this to work you will need to ensure the Scheduler (Task Scheduler) service is running on the destination machines.