SUMMARY
It adds about 30 seconds extra to login (via SDDM).


STEPS TO REPRODUCE
1.  Enable splash screen (either in the systemsettings or with "systemctl --user unmask plasma-ksplash.service")
2.  Logout from plasma and the log back in while taking the time
3. Disable splash screen (either in the systemsettings or with "systemctl --user mask plasma-ksplash.service")
4.  Logout from plasma and the log back in while taking the time

OBSERVED RESULT
When enabled, the splash screen adds about 30 seconds to login, while it takes a few seconds without.

EXPECTED RESULT
Negligible differences between the two cases.

SOFTWARE/OS VERSIONS
Kernel Version : 6.7.9.zen1-1
Plasma Version : 6.0.1-3
KDE Version : 24.02.0-1
Frameworks Version : 5.115.0-1
Qt5 Version : 5.15.12+kde+r10-1
Qt6 Version : 6.6.2-4
Wayland Version : 1.22.0-1
XOrg/Wayland Version : 23.2.4-2
Mesa Version : 1:24.0.2-2
LibVA Version : 2.20.0-1
VDPAU Version : 1.5-2

ADDITIONAL INFORMATION
Prior to version 6 I could log in almost instantaneously even with the splash screen on.