I guess it takes like 10 to 15 minutes, but maybe longer sometimes. We don't have a clock or any concern with time keeping when we have sex, it's been over 10 years now since we've been interested in the amount of time we spend. I need hands on my balls and perineum and touching me all over my ass, etc. for it to get really good. Subtle touches of the areas around my cock and I can literally feel the cum building up inside me. She also knows exactly what to do to pop me off, so she'll do that for a second and then switch to something more along the lines of edging me, and then go back to the thing that makes me cum in seconds. The back and forth is never boring and she knows the more she works it up the harder I'll cum. I shoot so hard it hits the back of her throat and gags her 9/10 times, and although it's a bit much for her, she LOVES when this happens and affirms for her that she not only did a good job, but got me to cum my fucking face off!
I guess for me, time melts away during blowjobs and I have no concern from start to finish. If she can't continue then she works in hands and sometimes fleshlight-type toys on my cock to make it even better.