It varies is the answer for sure but I'd say 5ish or 10 minutes is average. It's been longer, it's been (much) faster, but it totally depends on context. Energy levels, general excitement, consumption of booze or other intoxicants, etc.
My unfortunate observation is the longer I am with a partner the more comfortable I slowly become, and the less time I'm able to last.
Only 1 partner here, but absolutely been the case. I was soo in my head and focused on pleasing her and performing the first few months, I had issues climaxing. Now that we're almost 3 years in? Shit fires off in 5-10m on average.
I haven't been in a long term sexual thing yet, but I bet that as you stay with a partner longer, you've shared more about what turns you on and your partner gets better and better at doing those things.