Back when I was running: I NEVER get a runner's high UNTIL I hit the 4 mile mark.
Period.
The first 3.99 miles are MISERABLE. Painful, hard, yucky, miserable. But after 4 miles... I could run forever. (But if I stopped and walked, or slowed down at all any time in that 4 miles, the "clock" started over... but I could set my map by my 4mi 2nd wind.) There's no feeling except for "good". It's like you're floating. There is absolutely NO effort involved, no pain, you feel like you could go forever. ((Which is also why some people die running... that feeling lasts right up until there is no more potassium or free calcium, and the whole seizure and death thing that happens with long distance runners)).
Most people get the endorphin rush a LOT sooner... but some don't get it until even later. Even in the soon crowd... whether it's 1 minute, 5 minutes, half a mile, 2 miles... it's different for everyone.
Also... not everyone gets endorphin rushes from spicy food. Some do. Some don't. Here's a hint: Most people who don't like spicy food don't GET the endorphin rush... but neither do some people who like it.
That's great your husband has found a "thing" that he likes. But it doesn't mean that everyone's body is just like his.
One thing I've NOTICED (but haven't studied or looked up)... those with high pain tolerance tend to get their "2nd wind" or "runner's high" MUCH later than those with low pain tolerances. Anecdotally... the idea is that the more pain you can tolerate, the less your brain goes into 'emergency' mode to flood your system with painkillers.
It ALL about the 4th ventricle in the brain, and how it happens to function in your own particular neurochem and physiology.