Scrub the question above.
I just ran a more comprehensive search on previous posts and can see that there's a bug in this latest release of Macro Express, running with Windows XP.
You can't get a 24 hour clock in Set Schedule. You have to change your Windows regional settings to hh:mm:ss:t to give you a 12 hour clock with AM or PM.
I'm quite disappointed that I got no response from Insight to my question after 3 weeks.