On bootup I get a login Promt in the command line (no graphical user interface - GUI).
I can sign in and open files, but then the GUI begins to start.
If that would not be, the system cold boot faster, is a last of 20-30 sekonds.

Why?
How can i fix this?

Operating System: KDE neon 5.9.3 (Kernel 4.8.0-41-generic) 64-bit

What storage do you use to boot KDE neon(hard disk, ssd, flash drive)? Slower mediums result in longer times to boot, start applications, and sometimes even slowdowns with open applications!
KDE neon is usually one of the faster OSes to boot.

If
You want to change
from

booting into _GraphicalMode_User_Interface_
(Window System)

to

booting into _TextMode_User_Interface_,
(Command Line)

then

You have to change systemd's default.target
from

graphical.target

to

multi-user.target.

Alternatively, You could use the
systemd.unit=…
kernel command line option.

i´m using a SSD.

No, i want to boot the GUI.

Fastest?
neon boot´s on my Laptop in 1 Min. 25 Sek., Windows 10 in 13 Sek., YES 13 Sek. (Measured after GRUB2 Bootloader until GUI is visible).

If i go in GRUB2, select the recovery mode for neon and select boot neon. The neon boots much faster.
What can i do to speed up the boot time?