Just posting to reinforce what folks have said throughout this entire thread, because relaxing and patience are important parts of this hobby.
Over the weekend I brewed a strong Belgian dark. 'Twas my first high gravity beer. (I like to brew good drinking, borderline session beers and buy the big stuff.) Pitched late afternoon on Sunday. Multiple vials, but no starter. So underpitched, but not dramatically so. SG was 1.080/1.082.
Obviously it didn't take off right away. No signs of activity the next day. None day 2, either. By the 48-hour mark still nothing; popped the airlock and peered into the bucket with a flashlight. Thin layer of white film on top.
"Eh," I figured, "That means something is going on," and I walked away from it figuring nature would take its course.
At around the 72-hour mark, maybe a little past it, started to get airlock activity. It's been aggressively fermenting since.
No worries. Sometimes nature takes its sweet time. When all is said and done, chances are very good I'll have beer. And it may even be damn good beer.