The time when unit became active or started is printed after the "@" character.
The time the unit took to start is printed after the "+" character.

graphical.target @16.947s
└─sddm.service @16.920s +24ms
  └─plymouth-quit.service @8.726s +52ms
    └─systemd-user-sessions.service @8.675s +23ms
      └─network.target @8.628s
        └─NetworkManager.service @6.362s +2.264s
          └─dbus.service @5.723s +368ms
            └─basic.target @5.640s
              └─sockets.target @5.640s
                └─uuidd.socket @5.640s
                  └─sysinit.target @5.632s
                    └─systemd-udev-settle.service @2.165s +3.467s
                      └─systemd-udev-trigger.service @1.627s +533ms
                        └─systemd-udevd-kernel.socket @1.443s
                          └─system.slice @1.409s
                            └─-.slice @1.409s