Small update:
I find that when I return to the Manager window I have to move the window (a very small move is enough) so that the top bar updates. This is easy to do because the move bar is near the calendar icon.
Alternative method: Assuming you have Manager module window active. Use ALT+CONTROL + H to switch to main modules window. Change date as described. Hold down the ALT & CONTROL keys press S then H then S. You should now be back in the Manager as active window. Click the Calendar icon and dates should now be updated. This may be the faster method, it uses Harlekins built in macros to switch active windows.
As always only try this if you assume total responsibility for all effects. It works well
for me. Be aware that in Gemulator on Windows 98 changing the date in Harlekin as described
also changes the Windows 98 system date. That may or may not be desirable but it is easily
reversed either from Harlekin or in Windows.