There are hardware timer libraries for Arduino, for example, TimerOne, TimerThree, and FlexTimer2. But we don't always want to mess with hardware timer, only a soft timer library is needed.

Simple non-blocking timer library for calling functions in / at / every specified units of time. Supports millis, micros, time rollover, and compile-time configurable number of timers. This library ...

[ZHut] managed to bring these two worlds together by presenting how to make an Arduino blink an LED in conjunction with a 555 timer. We know, we know. It is hard to decide how to comment about this.