I'm already several minutes gone ...
When I unload in my wife's breasts or vagina for "round 1," I'm stilling still pumping 1-2 minutes after I go, and then I like to "stay there" for a few more. So by the time I get up and she starts to suck for "round 2," it's not nearly as sensitive and the "warmth" is nice -- typically getting me to "round 2" with a reduced load for her that's easier to take.
But yeah, when she takes me orally for "round 1," it is pretty difficult not to squirm or even chuckle from the sensitivity. But she's pretty good and not using her tongue for a few minutes until the sensitivity is lessened and she can start again. But typically if she's taken me in her mouth for "round 1," she's drooled it all over her DD chest -- so I like to unload in her breasts for "round 2." Of course, she likes to swallow at time (I'd rather her drool over her breasts, so she's been doing that more), so sometimes it's a 1-2 combo in her mouth.