Early in the year woodcocks often do only a single flight in the 
morning, and then again at night, so hearing them requires some focused 
attention.  At my location on Snake Mountain in western Addison County I 
seldom can hear the peents because I am upslope from the ground location 
of the birds.  But I hear them at the top of their flights.  It can be 
hard to find the time to wait around to hear them, due to one's normal 
schedule ... and not everyone can spend a lot of time out in the dark of 
night or twilight waiting for a single peent or twitter.

The timing is highly regulated by light quality, which helps us locate 
them via time of day.  Below are my records (2019 and 2016 combined) for 
the period March 18 to 31.   On several times in past years I have 
positioned myself beside an "inert" woodcock, which did nothing upon my 
arrival some 10-15 minutes prior to the expected first flight.  Nothing 
happened, until within a minute either side of the expected flight there 
suddenly was an explosion of wings and off would go the bird climbing 
higher and higher in display.

Starting at midnight the 24 hour day begins with night.  At the very 
beginning of any visible glow at a distant horizon (technically the sun 
is 12 degrees below the horizon) begins Nautical Twilight.  When the sun 
reaches only 6 degrees below the horizon Civil Twilight begins, and our 
eyes begin the perception of color for objects around us.  The next 
event will be the beginning of the sun's rise above the horizon.

Numerous birds are very responsive to these moments and transitions.  
Woodcock, now in their first arrivals, with a high degree of 
faithfulness make their first, and often only flight that we can hear at 
just over a third of the time distance from the beginning of Nautical 
Twilight to the beginning of Civil Twilight. I use 
http://www.sunrisesunset.com to easily obtain those times for my 
location.  Then if I want to be time efficient I know just when to go 
out and listen.  Also, if it is very stormy, windy, or otherwise noisy, 
I can be especially attentive to hearing the birds knowing almost 
exactly when to expect them.

If you live in an area where sunrise is blocked by mountains, the 
effective Nautical and Civil Twilight times will be delayed slightly.

The same process holds for hearing woodcocks in the evening.  Once the 
population territories are well established and everyone has arrived, 
I've found that from the beginning of evening vocalization/displaying to 
its conclusion spans about 54 minutes on average (at least here where I 
live.)  Of course you can always expect a maverick!

Ian
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Morning first-flight (usually the only flight) times relative to 
Nautical and Civil Twilight in late March, at 44 deg. North Latitude in 
Vermont.  At our latitude at this time of year Nautical Twilight is a 
constant 34 minutes in duration. ----

Minutes after the beginning of Nautical Twilight:

Mar 18     12
Mar 19     03
Mar 21     12
Mar 22     13
Mar 23     12
Mar 25     13
Mar 26     13
Mar 27     12
Mar 28     09
Mar 29     13
Mar 31     13

Minutes before the beginning of Civil Twilight

Mar 18     22
Mar 19     31
Mar 21     22
Mar 22     21
Mar 23     22
Mar 25     21
Mar 26     21
Mar 27     22
Mar 28     25
Mar 29     21
Mar 31     21