How to set a Christmas light timer

The direct answer: which procedure you follow depends on which of four kinds of timer you bought. On a mechanical dial you set the current time by rotating the dial to the arrow, then push down the pins covering the hours you want the lights on. On a digital 7-day timer you set the clock first, then program an ON time and an OFF time as a numbered event. On a photocell timer you set nothing but the run-time duration, because dusk is the trigger. On a smart plug you set a schedule in the app, ideally relative to sunset rather than to a fixed clock. Across all four, the three things people get wrong are the same: AM versus PM, failing to move the manual override back to AUTO, and never setting the clock at all.

Before you set anything: the two-minute checks

1. Confirm the timer is rated for what you are plugging in. A weatherproof outdoor unit rated 15 amps covers any LED display comfortably. Check the rating on the body, not the box.
2. Confirm it is an outdoor unit. An indoor timer in an outdoor receptacle is the same mistake as an indoor extension cord, and the housing is the whole difference.
3. Plug it into a GFCI-protected receptacle and press test and reset once before you program anything. A timer is the wrong place to discover a GFCI fault.
4. Set it up indoors first if you can. Programming a digital timer with cold fingers in the dark beside a flower bed is how people end up giving up on them.
5. Decide your window before you touch the buttons. Six hours covering dusk to bedtime is the standard answer, and the reasoning is in can you leave Christmas lights on all night.

A mechanical dial timer

The simplest kind, and the one that never needs a manual once you have done it once. A mechanical timer is a 24-hour dial with segment pins around its edge, typically at 30-minute resolution, and a switch with AUTO and ON positions.

1. 1

   Set the current time

   Rotate the outer dial until the current time of day lines up with the arrow or triangle marked on the body. The dial only turns one way on most units — do not force it backwards.

2. 2

   Push down the pins for the hours you want the lights on

   Each pin is a segment of the day. Pushed down means on. For a 5 pm to 11 pm window, push down every pin between 5 and 11. Leave everything else up.

3. 3

   Set the switch to AUTO

   This is the step people miss. In the ON position the timer is just an extension cord with a dial on it, and the lights stay on permanently.

4. 4

   Check it that evening

   If it switches an hour out, the dial was set an hour out. Rotate it to correct and the pins stay as they are.

A digital 7-day timer

More control, and the one with the most places to go wrong. The programming model is the same across almost every brand: a clock, then a list of numbered ON/OFF event pairs, then a mode.

1. 1

   Set the clock and the day

   Press CLOCK and set hours, minutes and the day of the week. Watch the AM/PM indicator — a display that reads 6:00 with no indicator is a display that could be either, and this is the single most common digital-timer error.

2. 2

   Open the first program slot

   Press PROG or TIMER once. The screen will show something like 1 ON. That is program one, its switch-on event.

3. 3

   Set the ON time, then the OFF time

   Enter your start time, press PROG again to move to 1 OFF, and enter the end time. A 5 pm to 11 pm window is 1 ON at 5:00 PM and 1 OFF at 11:00 PM.

4. 4

   Set the days the program runs

   Most units cycle through presets — every day, weekdays only, weekends only, or a single day. For a Christmas display, every day is almost always what you want.

5. 5

   Return to AUTO and verify

   Press CLOCK or MODE until the display shows AUTO rather than ON or OFF. Then press the override button once to confirm the outlet switches, and press it again to hand control back to the program.

If your display needs two schedules — lights until 11, inflatables off at 9 — use two program slots on a multi-outlet timer, or two separate timers. The comparison of the two formats is in mechanical vs digital timers.

A photocell or dusk-to-dawn timer

There is almost nothing to set, which is the appeal. The unit has a light sensor; it switches on when the ambient level drops and then either runs until dawn or runs for a selected number of hours.

• Choose the run-time setting, not true dusk-to-dawn, if your unit offers both. A 2, 4, 6 or 8-hour selector is the useful mode. True dusk-to-dawn is all-night operation by design.
• Site the sensor away from your own lights. A photocell that can see the display it controls will see its own light, decide it is daytime and switch off — then switch on again, in a loop. Point the sensor away from the house and away from a street light.
• Give it a night to settle. Switch-on will be a little earlier or later than you expect on the first evening, because the trigger is a light level and not a clock.
• Remember it tracks the season. This is the real advantage: as the days shorten through December the switch-on time moves on its own, which no fixed-clock timer does.

A smart plug

The most capable and the one that needs the most setup once. The important detail is to schedule relative to sunset rather than to a clock time.

1. 1

   Connect it on 2.4 GHz, before you mount it

   Outdoor smart plugs are 2.4 GHz devices. Pair it indoors next to the router, confirm it works, then take it outside — pairing beside a flower bed at the edge of coverage is where this goes wrong.

2. 2

   Set your home location in the app

   Sunset scheduling needs to know where you are. If the location is wrong, every sunset-relative schedule is wrong by the same amount all season.

3. 3

   Create a sunset-relative ON event

   Choose sunset with an offset — 15 or 30 minutes after is about right for a display to read properly — rather than a fixed 5:00 PM. The schedule then shifts itself through the season.

4. 4

   Create a fixed-clock OFF event

   Off should be a wall-clock time, because it is governed by your bedtime and not by the sun. 11:00 PM every night is the usual answer.

5. 5

   Use the second socket for a different schedule

   A dual-socket outdoor plug has two independently switched outlets. Put the inflatables on the one that goes off earlier.

The three mistakes

1. AM instead of PM. A display that comes on at six in the morning and goes off at midday has a 12-hour error in the clock, not a broken timer.
2. Left in manual ON. Every timer has an override, and every override has to be returned to AUTO. If the lights never go off, check this before anything else.
3. Clock never set. A digital timer out of the box thinks it is midnight on Monday. The programs will run — twelve or more hours out from where you wanted them.

If the timer is right and the display still misbehaves, the problem is upstream. Lights tripping the breaker and GFCI and outdoor lights cover the two faults that look like timer failures and are not.