You can either use the system time, i.e. the Mac’s system clock, or simulate the time in Lunar 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 lunar 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.
   

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