Analog configuration on the puck.js?

There's also now support in the LL libs for the ADC and the RTC, so if you wanted to measure pulse length in a low-power way you could use the button length example:

var ll = require("NRF52LL");
// Source of events - the button
// Note: this depends on the polarity of the physical button (this assumes that 0=pressed)
var btnu = ll.gpiote(0, {type:"event",pin:BTN,lo2hi:1,hi2lo:0});
var btnd = ll.gpiote(1, {type:"event",pin:BTN,lo2hi:0,hi2lo:1});
// A place to recieve Tasks - the RTC
var rtc = ll.rtc(2);
poke32(rtc.prescaler, 0); // no prescaler, 32 kHz
poke32(rtc.tStop, 1); // ensure RTC is stopped
// Set up and enable PPI to start and stop the RTC
ll.ppiEnable(0, btnd.eIn, rtc.tStart);
ll.ppiEnable(1, btnu.eIn, rtc.tStop);
// Every so often, check the RTC and report the result
setInterval(function() {
  print(peek32(rtc.counter));
  poke32(rtc.tClear, 1);  
}, 5000);

Nothing stops you hooking that up with the 'button press counter' example so you can then get the average button press length with time_button_pressed / button_presses