I had a 5hr booking once and he didn't want to leave the hotel room incase someone saw us.
I ended up getting in the shower with him and washing each other, giving him a back and scalp massage, foot rub and then moved on to the rude stuff, that was an hour gone.
If you don't mind clients going down on you and he is agreeable, encourage him to do this, then you can take some time to relax and just mmmm and aaaahhh occasionally. This could give you maybe half an hour, maybe more.
Then a slow bj, be teasing and drive him mad. Use long deep stroaks and use your tongue a bit. Either let him finish that way, or better yet whip on a condom and let him do some work! I could easily blow a guy for a full booking, and have done a full hour of oral only on a few occasions. As long as you keep it sensual and occasionally bring him just to the brink, he will love this!
Let him enjoy the post o glow, if you had sex join him or if you finished him orally clean up, offer him a glass of water, get one for yourself then its cuddles and chit chat and just like that you're at the 2.5h mark or maybe more!