A timer is an electrical item used in crafting.
The only current use for the timer is crafting a crafted timer.
Note that the timer cannot be used in a similar way to the alarm clock, in setting a time to emit a noise.
From newitems.txt (Project Zomboid directory/media/scripts/)
Weight = 0.3,
Type = Normal,
DisplayName = Timer,
Icon = Timer,
MetalValue = 7,