Why? Because I was shopping at walmart and noticed they had timers on sale so I picked some up, and decided to use one for this. It also gives the added benefit of having a GFCI for extra protection of your outside lights and helps protect in the event of a short of your lights.
DISCLAIMER: I am not responsible for any of you killing and/or hurting yourself or others while attempting this project. This should only be done by someone with some experience in electronics.
Step 1: Parts & Tools
You will need:
1X Digital Timer ($17.94)
1X GFCI ($14.99)
1X Outlet Cover ($2.59)
1X Outlet Box ($2.09)
2X Romex Clamp (bag of 5 $1.69)
1X 40 FT Extension Cord ($7.78)
2X Wire Nuts (my timer had several in it) ($0.00)