Question about loot spawning (not a rant, a real question :) )

Hello SCUMbags! So, yesterday I was at the underground military airbase at D4. The server was about to restart, so I thought it would be nice to get all the juicy loot as it restart by login off in there. But no. It wasn't at all. I started looting just after the server restarted and the loot was everything but juicy. In fact it's the worse run I ever had.
So the question is (or are:) ) : is there a delay for loot to spawn back when the server gets online? And does my presence delay the loot respawn around me? Or else I don't understand? I just want to know how their system work to help my timing with looting. My teammate said he observed the same issue when login inside bunkers after a restart.
Thank you.