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°
2018- 4-25 Wednesd  5: 8  20:35   35.1   13.26     2.0   8.54   28.3
        26 Thursda  5: 6  20:37   35.3   13.58     2.2   8.48   28.9
        27 Friday   5: 4  20:39   35.4   13.90     2.3   8.42   29.4

Average for   3 days
from   3 values is  5: 6  20:37   35.3   13.58     2.2   8.48   28.9

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  d25.04.2018 t02:28 l16.6 f49.2 ut2  h-6 n2 i1