For me if i haven't cum in a while it will obviously be quicker.  Some reason when i go to massage parlors i dont last that long.  But for me in general i  can usually last the whole hour, but I cant go 2 rounds unless i book 2 hours.

In my much, much younger days, I booked a doubles at a brothel on 2d Avenue in the 50s.  My first double session.  Two gorgeous young women in lingerie running their hands over me.  Popped before penetration...ooops!  

3 seconds ...

Most guys come in excited and have at least a raging semi the moment they get through the door. Totally fine .
This one guy was way more excited than I realized.  
After we're both nude and had quite a nice bit of heavy petting, light nibbling, kissing etc I move to go down on him.
I was literally just starting to get a taste of his manhood and he started cumming like a geyser.....total 2 licks .

... I can see why I might be quick to, uh, express my appreciation...

.....I can stay hard after I cum.  It is always interesting to see if a provide will keep going after I cum.  There have been a few, particularly in CG, that will keep going until they get off.

Using a cock ring has allowed me to have multiple orgasms, not pops, but orgasms.  First time that happened a provider was riding me and I slowed her down, saying I think I am cumming.  Actually, with some focus and the ring, I had a small orgasm without ejaculation.  I looked her in the eye when the moment pasts and said, kind of but lets keep going. Her response, bless her heart, was enthusaistic and she road me for several minutes.

On the other hand, a good BBBJ without the ring, I am done in moments. I must coach my partner so as not to bring on the eruption too soon.