I believe the Fences process slows a boot time by 0.3 of a second - about the blinking of an eye.
What you see however is the timing of 3rd party processes imposed upon Developers by Microsoft, ie only after the OS has completed loading - the true time it takes, not the artificial timing of desktop icons appearing before the boot has completed.
The only 'slowing' of your system is that 0.3 seconds....and the impression of "delay" as icons appear at the end of the boot, not somewhere in the middle of it...