From the introduction:

Electrical timers are superior to delays that use candles, incense or cigarettes. Electrical timers have significantly longer delay times. When electrical timers are carefully constructed, they are more reliable. Each one can be tested repeatedly until you are certain that it will work. Electrical timers are easily protected from wind and
rain, whereas even a mild breeze can be a problem for candles and incense.

This guide has recipes for two electrical timers, the Old-Fashioned Kitchen Timer and the SCR Digital Timer. Both recipes have been greatly expanded to give extremely clear and detailed instructions. Our goal has been to eliminate ambiguity from the directions and to provide as many helpful tips as possible. You don’t need prior experience with electronics. You need only practice some with a soldering iron. As long as you pay attention to details and do the proper testing, you’ll be able to construct highly reliable timers.

The Old-Fashioned Kitchen Timer is relatively quick and easy to construct. The SCR Digital Timer takes much longer to build, especially the first few times, but it is worth the effort. At the target, it can be positioned and activated with unparalleled speed and safety. In addition, the SCR Digital Timer is extremely precise – down to the minute, and even down to the second, depending on the timepiece. With that level of precision, you can guarantee that multiple incendiary devices will ignite at the same time. Simultaneous ignition is especially important in situations where you expect firefighters to arrive quickly. If ignition is not simultaneous, the first fire may bring firefighters onto the scene before the other fires have a chance to do damage.

There are two other timer recipes that have been passed around. Both have serious drawbacks and should no longer be used. One recipe uses the hour hand on a wind-up wristwatch to push two wires together. It is terribly imprecise and most wristwatches are unable to perform the job. The other recipe uses an alarm clock that plugs
into an electrical outlet. (It must be an alarm clock with a battery backup.) This type of alarm clock shuts off its display when unplugged, creating complications for the saboteur. Another problem is its reliance on a REED relay, which is not a solid state component and not as resilient as an SCR. The SCR Digital Timer is more foolproof and easier to use.

We hope you find many good uses for these timers. Enjoy.

–37 pages B&W: Setting Fires With Electrical Timers- An ELF Guide
http://325.nostate.net/wp-content/uploads/2014/09/elf-guide.pdf