Pyrosium is dumb as heck

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I was able to set up a pyrosium mix that would go off in a predetermined amount of time (the catch
being that the timer is started the instant you take it out of the reagent heater).

How did I even forget to mention that you're tied to the heater. It would be much more useful if it only started heating the moment it came into contact with another reagent; think self-heating cups.

Just put two of the ingredients into the beaker, keep a third in a dropper, and add it to the beaker at the proper time. It's a little inconvenient, but if you're just looking to make a smoke bomb or something, timer/igniter assemblies are more convenient, more precise, and actually easier to get your hands on. For pyrosium, it's better to look at exotic uses that beaker assemblies can't do - like setting off reactions in someone's body.