Arch Linux

Sure the config file differs for a different use case. But there should be no delay though. Please check dmesg or journal with timestemp where the delay occurs. Feel free to diff the config files. It boots fine for me at all my three systems without any delay.

With linux-kernel it so fast (within seconds).
With linux-lts it is delaying at NetworkManager-dispatcher or systemd-hostnamed or crng.

I have disabled the NetworkManager units, but without success, maybe it is a "crng init issue" as described in  bug 58355 .

I use a mobile connection after the startup in KDE (usb0 device), so there is no network connection during startup.
Can you please test your system without a network connection during startup.

=== Linux LTS ===

Jan 1 17:34:10 tv nm-dispatcher[620]: req:2 'connectivity-change': new request (1 scripts)
Jan 1 17:34:10 tv kernel: IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready
Jan 1 17:34:10 tv nm-dispatcher[620]: req:2 'connectivity-change': start running ordered scripts...
Jan 1 17:34:10 tv polkitd[629]: Started polkitd version 0.116
Jan 1 17:34:10 tv dbus-daemon[450]: [system] Successfully activated service 'org.freedesktop.PolicyKit1'
Jan 1 17:34:10 tv systemd[1]: Started Authorization Manager.
Jan 1 17:34:16 tv NetworkManager[451]: <info> [1546360456.3229] manager: startup complete
Jan 1 17:34:20 tv kernel: kauditd_printk_skb: 72 callbacks suppressed
Jan 1 17:34:20 tv kernel: audit: type=1131 audit(1546360460.588:57): pid=1 uid=0 auid=4294967295 ses=4294967295 msg='unit=NetworkManager-dispatcher comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Jan 1 17:34:40 tv kernel: audit: type=1131 audit(1546360480.049:58): pid=1 uid=0 auid=4294967295 ses=4294967295 msg='unit=systemd-hostnamed comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Jan 1 17:35:02 tv kernel: random: crng init done
Jan 1 17:35:02 tv kernel: random: 7 urandom warning(s) missed due to ratelimiting

=== LINUX ===

Jan 1 18:24:52 tv kernel: IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready
Jan 1 18:24:52 tv sddm[630]: Initializing...
Jan 1 18:24:52 tv sddm[630]: Starting...
Jan 1 18:24:52 tv sddm[630]: Logind interface found
Jan 1 18:24:52 tv sddm[630]: Adding new display on vt 7 ...
Jan 1 18:24:52 tv sddm[630]: Loading theme configuration from ""
Jan 1 18:24:52 tv sddm[630]: Display server starting...
Jan 1 18:24:52 tv sddm[630]: Running: /usr/bin/X -nolisten tcp -auth /var/run/sddm/{e399aa8d-a3be-4ea2-a6af-ae5ccc0d1399} -background none -noreset -displayfd 17 -seat seat0 vt7
Jan 1 18:24:52 tv dbus-daemon[538]: [system] Activating via systemd: service name='org.freedesktop.PolicyKit1' unit='polkit.service' requested by ':1.1' (uid=0 pid=540 comm="/usr/bin/NetworkManager --no-daemo>
Jan 1 18:24:52 tv kernel: IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready
Jan 1 18:24:52 tv NetworkManager[540]: <info> [1546363492.2897] ovsdb: Could not connect: No such file or directory
Jan 1 18:24:52 tv systemd[1]: Starting Authorization Manager...
Jan 1 18:24:52 tv nm-dispatcher[610]: req:2 'connectivity-change': new request (1 scripts)
Jan 1 18:24:52 tv nm-dispatcher[610]: req:2 'connectivity-change': start running ordered scripts...
Jan 1 18:24:52 tv polkitd[681]: Started polkitd version 0.116
Jan 1 18:24:52 tv systemd[1]: Started System Logger Daemon "default" instance.
Jan 1 18:24:52 tv systemd[1]: Reached target Multi-User System.
Jan 1 18:24:52 tv systemd[1]: Reached target Graphical Interface

Have you tried the mitigation's suggested for  FS#58355  to see if it is related e.g. adding the boot option random.trust_cpu=on assuming the CPU supports RDSEED or RDRAND or using haveged or pressing random keys to generate entropy?

Thank you very much for the hints.

The boot parameter "random.trust_cpu=on" for grub did not work, but "pressing random keys" on the keyboard helps immediately.

So I use haveged service now, and it works fine without typing.

Or is it better to use rng-tools ?

CPU: Intel(R) Core(TM) i5-2400 CPU @ 3.10GHz

i5-2400 is Sandy Bridge so does not support the RDRAND instruction introduced with Ivy Bridge.
See https://wiki.archlinux.org/index.php/Rng-tools unless you have some other hardware RNG then haveged is recommended.