You can change many of the Clock settings without using the Properties window by moving the pointer anywhere within the open Clock window and typing the following keyboard accelerators:
Type 1 to set the 12-hour display mode if the current Clock is digital.
Type 2 to set the 24-hour display mode if the current Clock is digital.
Type c to toggle the Clock face between analog and digital displays.
Type d to toggle the Date display on and off.
Type i to toggle the icon face between analog and Roman.
Type s to toggle the seconds display on and off.
Type S to set the stopwatch. Type S again to start the stopwatch. Type S a third time to stop the stopwatch. You can then type S to reset the stopwatch again, and so on.
Type c when you want to reset the Clock to the normal clock display.
Type t to toggle the time zone between local and other. You must have a valid Other time zone set on the Properties window for this to work.
Note that you can have more than one Clock running at a time. This is useful if you want one clock to display the time and another to display the Stopwatch.