.
....
it's per ad, you don't have to receive any clicks just the 500 impressions.
not totally, i need something else in addition. It is either time, budget or clicks 
weird, I had 2 safe ads last week that both reached 500 impressions without a single click and both showed a (shitty) relevance score. I guess inconsistencies like this are just a part of the game with FB lol
in that case it is time 