nRF52: Time from calling __WFI() to HFINT turn off?

[CurtisHx]

Assuming that all peripherals that require the high frequency clock are disabled / turned off / stopped, how long does the HFINT oscillator run after calling __WFI()?

And if it's greater than 1ms or so, is there any way to shut it off faster?

[CurtisHx]

If HFCLK is already powered down by the time __WFI() is called, then what's the CPU running off of?

[CurtisHx]

I'm working on a project where we are trying to squeeze every last electron we possibly can from our battery, since the device is essentially disposable. Once the battery runs out, the device is dead. A few 100uA for a few milliseconds can mean a few months less battery life.