There are of course exceptions to every rule. Sam here gave her man an amazing 20 minute blow job. Strategically alternating her mouth and hands to keep him on the edge as long as possible. There just wasn't enough in the plumbing to give her all that she wanted.
You don't want to disappoint her or should I say yourself do you? One thing you can do to avoid this is to drink enough water to keep yourself hydrated.
Just for a change of pace, give me 30 quick strokes. Two every second. Go. I'm timing you.