I've experienced hangfires, but only in rifles. These have occurred with handloads where I used a powder that may have been recommended in a load manual but was not the best powder choice for the load combination, or perhaps the powder charge was the recommended minimum.

Most of the time this has been with cast bullet loads where much lower powder charges are recommended than the suggested charges for jacketed bullets. In every situation, the "hangfire" fired very quickly after I pulled the trigger; the lapse between pulling the trigger could not be measured in seconds. It would be a much smaller measurement unit than seconds, whatever that is called.

A round firing after ten or twenty seconds? Possible, I suppose, but unlikely. I've never experienced it in more that fifty years of handloading a lot of rifle and handgun cartridges. As I recall, I think I had a hangfire or two with some old factory or military ammo, but that's been a while.

The best example of a hangfire I can recall was more than ten years ago when developing some cast loads for a rifle in .375 H&H Magnum. This is a huge case and whatever powder I was using should have been suitable but the load was susceptible to hangfires. Switching to a magnum primer solved the problem in that instance.