I’ve been away from Squeak for a long time but I don’t think Schedule does what you want. I browsed the code a bit and it seems to be more about /storing/ a schedule rather than /executing/ one.
John Pierce wrote a package called Scheduler which I used with great success many (many) years ago. The SqueakMap entry still exists but the file links are dead. I have attached my latest version of that package. I tried it out in Squeak 5.2 and it seemed to work but I can’t make any promises. I don’t think it will have the same problems as a long Delay since its main loop seems to check for runnable tasks every 1/4 second.
BTW, to load the MCZ you can use the File List (under Tools).
Best,