Following page shows GE 15075 timer and manual.
Page also shows close-up image of pins used to set on-off times.
http://waterheatertimer.org/GE-timers-and-manuals.html#15075If this is not your timer, then add a comment with description of your timer.
To set timer:
Rotate dial clockwise until current time lines up with arrowhead located on inner dial
Click
pins in and out to set on-off times.
Pins out, lights ON
Pins inward, lights OFF
I use pointed fingernail file to click pins in-and-out.
Timer switch is located on top of timer.
Set switch to TIMER ON
Turn lamp on, and leave lamp ON.
Make sure bulb is working.
Plug lamp into timer.
Plug timer into wall outlet.
To double check timer functions manually rotate timer dial clockwise to watch light turn on-off.
You can also take advantage of fixya phone support.
Fixya expert will walk you through the steps for a price.