LOST THE SETTING INSTRUCTIONS OF MY TIMEX MODEL NO. 12/874 (TX12874X)

I couldn't find a manual for your Timex, but here are the setting instructions:

Clear the timer by pushing hour and minute at same time. To set current time, hold time button down and push hour. Then hold time button down and push minute.
To set the time for light to turn on, hold the ON button down and push hour until it gets to the hour you want it on (same for Minute). To set time for light to go off, hold the OFF button down while you set the hour and minute.