How do I wire GE# 15351 24hr mechanical timer switch for 110 volt outdoor landscape lights

SOURCE: How do I wire my GE 15306 timer to 1 110 volt line

The Black hot wire from your house supply goes on the terminal below the L and 1.

The White neutral wire from your house supply goes to the terminal below the X.

Connect a White neutral wire from the terminal below the X to your neutral on your load.

Connect a Black wire from terminal #2 to the Black on your load.

This wires up both your timer clock and will turn on your device, too.

SOURCE: how do I wire a double pole double throw 240 volt

You posted under GE timer, but added the brand name Intermatic.
GE and Intermatic timers are totally different.
Wiring below is for GE and will not apply to Intermatic.

Step 1) lets cover basic GE timer wiring for 240Volt load.
Be sure to set dip switches BEFORE applying power.
Step by step illustrations show on following link.
http://waterheatertimer.org/How-to-wire-GE-15207-timer.html

Step 2) Load wires exit GE timer.
There are two Hot wires and 1 bare ground wire.

Step 3) Wire the outlets: You have 4 240Volt plugs.
This could mean a receptacle-type outlet like a clothes dryer outlet or air conditioner outlet.
Or it could be a twist-lock receptacle or extension-cord-type stage plug.
In all cases, look at screw color on device.
Connect Hot wires to brass colored screws.
Connect ground wire to green screw.

Step 4) Calculate total Load
Manual appears below: Look at Normally Open contacts. These contacts turn ON when timer turns ON.
http://waterheatertimer.org/15087-15207-56922-Manual-eng.pdf
Total load on all 4 plugs cannot exceed 2 HP
Generally, a 30 amp timer is rated for max 24 Amps or 6 amps per each of the 4 plugs.
Volts x amps = watts.
Take total watts and divide by 240Volts to get amps.

Add a comment for more free help.
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SOURCE: GE 56941 24-Hour Outdoor Timer Switch: how do you wire this GE timer 56922 ?...

Open following links for GE timers and wiring:
http://waterheatertimer.org/GE-timers-and-manuals.html
http://waterheatertimer.org/How-to-wire-GE-15207-timer.html

GE box timers can be wired many different ways to control single-loads, multiple loads, 2-speed motors, 120V, 208V, 277V, 240V, 440V, 24V.

Add a comment and say exactly what you are wiring, and what voltage you are using for more information.