Timers

Overview
A timer is a type of contraption in Super Mario Maker that triggers an input or opens a path after a certain amount of time passes. They can be activated like a Question triggered contraption or an Automatic activator.

Shellmet timer
A shellmet timer consists of a triggerer connected to a row of brick blocks, which is connected to an input contraption segment, or some other device.

Wiggler trigger
A wiggler triggler utilizes the fact that big enemies will trigger P-Switches. The simplest type of wiggler trigger is just a big wiggler pressing a P-Switch. More complicated wiggler triggers create platforms that become solid when the switches are triggered, and have more switches under the platform. These will extend the P-Switch timer.

Skewer clocks
A skewer clock uses a skewer to destroy blocks until it triggers an input. They can either be built horizontally or vertically, and can trigger a P-Switch, POW block, key, or another contraption. More images can be found in the gallery at the bottom of the page.

Bob-omb timers
A bob-omb timer utilizes the fact that a fire source can explode a bob-omb. These contraptions have many variations, as there are many different fire sources in SMM. Sometimes, bob-omb timers use a bob-omb on a track to extend the timer, although it's not needed. More images can be found in the gallery at the bottom of the page.

Uses
Timers are usually used to make Mario need to survive a boss for a certain amount of time.

In addition, Mario could have to accomplish a task within a certain period of time. For example, jump around and collect 100 coins in 20 seconds