Multiple times a second, if your pool of hardware is "all the internet connected hardware in the world"! Neat experiment.
Also, FWIW that experiment will include people subject to bit errors in DRAM, not just in the CPU- and I would even guess that bit errors are more common in DRAM than SRAM given their electrical characteristics (a tiny floating capacitor vs. two inverters driving eachother)
Bit flips aren't solely caused by radiation- it could also be caused by clock skew or a failing crystal oscillator on an overheating router or something...
Also, FWIW that experiment will include people subject to bit errors in DRAM, not just in the CPU- and I would even guess that bit errors are more common in DRAM than SRAM given their electrical characteristics (a tiny floating capacitor vs. two inverters driving eachother)