A pinched tube can just sit there like a ticking bomb. Last year I changed my front tire 2 weeks before a tour. On the 3rd day of the tour, my tire suddenly starting making a funny noise so I pulled over and discovered the tube was just poking out from between the rim and tire but hadn't blown yet. I quickly deflated it, worked the tube back inside the tire, and re-inflated. I got lucky, no blowout! I probably did 400-500 miles before it showed up, though!