36 hours at least through some of my pins get no impressions as well. I assume it depends on the account, board and URL. If all these factors have a good engagement score, then pins are spread faster. If your account and website are completely new and you're not a business, I doubt Pinterest will spread your pins until they ensure your pins are worth exposure.
The 36 hours I assume it is the time their crawler takes to find your pins and evaluate them, moreover it is the time given for Pinner to adjust/delete new pins.