Length of the Night

as an interval between the PM and AM moments of Sun passing a given angular height (default -6°, for the ``civil night''):

Year:   Month:   Day:
Longitude: (western as -)   Latitude:
Your Time - UTC:  h
The relevant angular height of Sun is degrees
next days will be computed as well,
with a step of day(s).
   save settings    use my saved settings

Another option is to use your own command line (ev. overriding all previous data):

(`?' gives help). 

The centre of Sun is at a place with coordinates [Lambda=16.6°, Phi=49.2°]
 in an angular height of h =-6.0°
 in the following morning and evening moments (given in UTC+ 2h):

 year-month-day  morning evening twilight decl.  >mean  night   A-W
                       h:min     / 1 min   /1°   /1min   /1h    /1°
2021- 5-18 Tuesday  4:27  21:13   39.3   19.65     3.5   7.24   39.7
        19 Wednesd  4:26  21:14   39.5   19.87     3.5   7.19   40.1
        20 Thursda  4:24  21:16   39.7   20.08     3.4   7.14   40.5

Average for   3 days
from   3 values is  4:26  21:14   39.5   19.87     3.5   7.19   40.1

Meaning of remaining columns:
 Twilight    is an interval to/from h=-0.8°
 Declination of Sun is given for the moment of local mean noon,
 >Mean       says how much is the Sun ahead of the mean time,
 Night       is the time the Sun travels below h,
 A-W         is departure of solar azimuth from the west when at h afternoon.

This is a result of the programme nights (available as a part of a package pas_jh.zip (1.2 MB) -- the needed Pascal units themselves are unzipped within this directory, the whole tree of my programmes within this directory) with a command line: 
nights  d18.05.2021 t03:27 l16.6 f49.2 ut2  h-6 n2 i1