Does a timed reaction "ready indicator" paper exist?

I'm trying to see if such a thing exists in paper form that upon activation, changes colour or "indicates" after a set configurable amount of time. 


In other words a litmus or pH paper that can act as an egg timer. I'm by no means a chemist so please excuse my lack of protocol.




I'm not aware of any commercially available examples, but I know that the speed of a fluid wicking through a paper microfluidic device has been [used](http://pubs.acs.org/doi/abs/10.1021/ac1005537) for timing. I'm also reminded of [pencil detonators](http://en.wikipedia.org/wiki/Pencil_detonator), dating back to WWII, where the time taken to dissolve a lead wire is used for timing. Since electronic timing is now so cheap, easy, accurate, and reliable, I'm not surprised that chemical timers have pretty much died out. There are a number of chemical phenomena that could be exploited for timing, but unless you need a huge number of cheap, one time use timers with relatively poor accuracy, there are probably better choices.


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