You can either use the system time, i.e. the Mac’s system clock, or simulate the time in Solar Eclipse Maestro by opening the Simulated Date & Time dialog.

1. To set the time to the Mac’s system clock choose Observer > Current Time… This what you’ll use during the solar eclipse.
2. Adjust the clock’s offset if necessary by choosing Setup > Clock Adjustment…
   
3. When a GPS is connected with a fix on the satellites and the Setup > Use GPS time option is activated, then the clock error adjustment is constantly updated based on time readings from the GPS. In that case the field can’t be modified.

1. To simulate the time choose Observer > Simulated Time…
2. Fill in the required fields (see below if you want to use the 24-hour mode).
   

Simulating the time enables you to fudge the clock without affecting the Mac’s system time to allow easy rehearsal long before the solar eclipse.

1. If you want to display the UTC time in 24-hour mode when the system’s current setting is in 12-hour mode, i.e. AM/PM, then go to System Preferences and select the International (Tiger and Leopard) or Language & Text (Snow Leopard, Lion, Mountain Lion and Mavericks) control panel.
   
2. Then select the Formats (Tiger and Leopard) or Region (Snow Leopard, Lion, Mountain Lion and Mavericks) tab.
   
3. Finally click on the Time Customize… button and use the settings below.
   
   You’re done, the UTC time will now be displayed in 24-hour mode.