That's unlikely how it actually works on Google's site. Google doesn't have to connect to an advertiser's network, they already have the ad information and all

That's unlikely how it actually works on Google's site. Google doesn't have to connect to an advertiser's network, they already have the ad information and all targeting and bidding information, so they can mostly compute the results ahead of time and only do last minute checks for winners based on, for example, whether the most likely winners have exceeded daily limits and such.