I've tested this before and didn't see much, if any of a difference compared to the microSD card included with the camera. You might see a teeny tiny shorter boot-up time, but after that all the camera operations will still perform at the same pace. In other words, a faster microSD certainly won't speed up offloading footage or anything like that.
A healthy boot time with a Chronos 1.4 is about 50 seconds from pressing the power button to being able to start recording.
If you're observing 3 to 7 minute startup durations, it sounds like you are experiencing a different issue. Occasionally the camera can get stuck in a loop of restarting itself. It should self correct, however may very well take up to 7 minutes. I recommend checking the Util > About > Last Shutdown Reason for clues when you observe that long of a startup.
A healthy shut down would be indicated by "97: PwrBtn, Software, PMIC Ack", and should only take about 10 to 15 seconds.
If you're seeing anything else, such as "5: Watchdog, PMIC Ack", then I suspect this is a bug in the software. Try rebooting the camera after one of those lengthy startups, and see if it hasn't self corrected to under 1 minute.
