How long does the Wake pin have to be high for IMP to wake?

Imp Pin Mux says Imp does not wake on a rise, but on a high state.
How long does it have to be high to wake up the imp?
I can choose between 250us and 1s.

I can’t find it in the docs right now, but I believe it has to be high for a couple of ticks of the 32kHz clock. I’d pick 250us; the imp cannot sleep if the line is high so 1s may be limiting in the future.

The imp will wake up on a very narrow pulse, but if the pulse is under 20ms then it can’t reliably be detected if a timer wakeup happens at the same moment. So if your application relies on never missing a pin wakeup under any circumstances, make it 20ms or more.