It takes me a while to cum like that... usually. I've gotten a blowjob and the person sucking me has gotten me off in a few minutes and something I had to learn not to be embarrassed about.
My wife has become very good at Blowjobs, but gets frustrated as it can take me a long time to cum. 30 minutes is her time line then she wants me to finish .
It totally depends upon who is giving said BJ. I have had women suck on my peen for 30+ minutes and we're not going to get there. I'll usually stop them around 15 minutes so they don't have severe jaw pain. It takes a really sexy woman, a mind bender and good cock sucker to get me off with just oral. I happens. Just not that often.