Lights continue to go off

Intermatic make HB51 timer.

If this is not your timer, then add a comment.
To set for ON at dusk, and off 8 hours later, rotate dial to the number 8.
Timer turns on automatically at dusk.
Timer set to 8 hours will start countdown when timer turns ON > and 8 hours later timer will turn off.

Make sure timer is turned away from lights so photo-eye doesn't receive feedback.
Feedback is when the photo eye gets too much light, and then timer thinks it's dawn, so lights turn off, and a moment later photo eye thinks it's dusk again and lights turn on again.
Feedback from lights will cause timer to reset the 8 hour countdown.
A car pulling in the driveway can cause feedback.
If the timer resets because of feedback, it begins the 8 hour countdown again, so the lights will not turn off until dawn.

You can test timer by putting black tape over photo eye, and then timer will turn on.
Set timer for 2 hours for example and then check if timer turned off 2 hours later.

If timer is not functioning correctly, then timer is defective.

manual for HB51RC
http://www.intermatic.com/%7E/media/files/intermatic/products/instructions/timers/hb61rc%20-%20english.ashx
See timer at Amazon
http://www.amazon.com/Intermatic-HB61RC-Digital-Outdoor-Control/dp/B00004W4X5


Plug timer into outlet
Plug lights into timer
Timer turns on automatically at dusk + override lets timer run during daylight hours
Timing cycle repeats each 24 hours
Use selector button to set timer
Timer must be reset after power outage or after unplugging timer.
Rotate selector button and choose one of following

F > Lights are OFF
O > Constant ON
1 through 9 > timer turns ON at dusk and turns OFF 1 to 9 hours later
d > timer turns ON at dusk and OFF at Dawn
1. through 9. > timer turns ON immediately and then turns OFF 1 to 9 hours later
Maximum wattage 1000
50 mini-bulb-string of Christmas lights is 25 watts

I see nothing in the manual that says 'outdoor use only' EXCEPT timer runs on photoelectric eye.
Timer turns ON automatically at dusk, so if timer is inside, and indoor lights are ON, then timer stays OFF.

http://www.intermatic.com/~/media/files/intermatic/products/instructions/timers/hb51rc%20-%20english.ashx

http://www.intermatic.com/products/timers/consumer%20outdoor%20timers/electromechanical%20timers/hb51rc.aspx


To use timer outdoors.
Plug timer into wall.
Timer turns ON automaically at Dusk.
Rotate dial to set how long timer will stay ON.
Set timer to turn OFF 2 4 6 8 Hours after dusk
Set timer to turn off at dawn
Set timer to ON so lights are ON full time
Set timer to OFF so lights are off full time.

I don't think it is supposed to be in the "on" position when setting it up.
Turn dial to "off".
Then plug timer into grounded outlet.
Turn dial to 2, 4, 6 or 8 hours to run after dusk.
Plug in your outdoor lights.
Wait until dusk.
Let us know if this works.

http://www.intermatic.com/products/timers/consumer%20outdoor%20timers/electromechanical%20timers/hb51rc.aspx


1. Turn dial selector to the "off" position and
plug timer into three conductor outdoor outlet.
2. Turn dial selector to timing interval
desired (i.e., 2 Hrs, 4 Hrs, 6 Hrs, 8 Hrs,
dusk to dawn, etc.).
3. Plug outdoor lights into Easy-Set™ Timer -
lights will turn on automatically at dusk.
4. Lights turn off 2 4 6 or 8 hours later
depending on dial selection

Woods makes several outdoor timers:
http://waterheatertimer.org/Woods-timers-and-manuals.html

Image that shows with this post is Woods model #49647.
Below are instructions for #49647 timer.

If your timer is different, add a comment with model number and I'll post instructions for that timer.

Woods model #49647 is outdoor timer with photoelectric control that turns timer ON at dusk.
There are 4 possible settings that show on dial.
Rotate dial to make timer selection.
OFF = timer is OFF full-time until you change dial.
ON = timer is ON full-time until you change dial.
Dusk-Dawn = timer turns ON at dusk and OFF at dawn
2, 4, 6, 8 hours = timer turns ON at dusk, and turns OFF 2, 4, 6, or 8 hours later.

http://www.intermatic.com/products/timers/consumer%20outdoor%20timers/electromechanical%20timers/hb51rc.aspx

HB51 appears to be an automatic timer
Capacity is 1000Watts
Your lights are on so the circuit has power
I don't see any troubleshooting steps
It gives you a choice how many hours your lights stay on after dusk

You might try changing the selector to a different stay-on hour.
Turn timer off and unplug and then re-plug timer to see if it re-sets.

Otherwise, it looks like the photocell or 'timer brain' stopped functioning.

manual for HB51RC
http://www.intermatic.com/%7E/media/files/intermatic/products/instructions/timers/hb61rc%20-%20english.ashx
See timer at Amazon
http://www.amazon.com/Intermatic-HB61RC-Digital-Outdoor-Control/dp/B00004W4X5

Plug timer into outlet
Plug lights into timer
Timer turns on automatically at dusk unless you set override feature shown below

Timing cycle repeats each 24 hours
Use selector button to set timer
Timer must be reset after power outage or after unplugging timer.
Push selector button and choose one of following

F > Lights are OFF
O > Constant ON
1 through 9 > timer turns ON at dusk and turns OFF 1 to 9 hours later
d > timer turns ON at dusk and OFF at Dawn
1. through 9. > timer turns ON immediately and then turns OFF 1 to 9 hours later
Maximum wattage 1000
50 mini-bulb-string of Christmas lights is 25 watts

From these instructions, you should push button until 6 displays. Timer will turn ON at dusk and turn OFF 6 hours later
If timer.
If you want timer to turn ON immediately and turn OFF 6 hours later, push button until 6. shows in display.

If timer does not display or does not operate correctly, then timer is suspect. Return timer for another one.

manual for HB51RC
http://www.intermatic.com/%7E/media/files/intermatic/products/instructions/timers/hb61rc%20-%20english.ashx
See timer at Amazon
http://www.amazon.com/Intermatic-HB61RC-Digital-Outdoor-Control/dp/B00004W4X5

Plug timer into outlet
Plug lights into timer
Timer turns on automatically at dusk + override lets timer run during daylight hours
Timing cycle repeats each 24 hours
Use selector button to set timer
Timer must be reset after power outage or after unplugging timer.
Push selector button and choose one of following

F > Lights are OFF
O > Constant ON
1 through 9 > timer turns ON at dusk and turns OFF 1 to 9 hours later
d > timer turns ON at dusk and OFF at Dawn
1. through 9. > timer turns ON immediately and then turns OFF 1 to 9 hours later
Maximum wattage 1000
50 mini-bulb-string of Christmas lights is 25 watts

I would unplug the timer. Change the setting to 6 hours then plug back in.