To measure boot times use
systemd-analyze
Result should look something like:
Startup finished in 2.463s (kernel) + 53.052s (userspace) = 55.516s
To see list of processes and how much time they take when booting up use:
systemd-analyze blame | head
If you want to visualize the boot process in .svg image use:
systemd-analyze plot > boot_process.svg
And finally when you want to mask a process in systemd (make it invisible and not bootable via systemd) use:
systemctl mask SERVICENAME.service