Lets imagine a girl who is a virgin and consents to have sex with her boyfriend.....she is scared and finds she is uncomfortable. She tells her boyfriend to 'stop' or 'that's enough, I need to go home now' or whatever. He should cease what he is doing immediately, it doesn't mean he should continue for another 15 seconds, 90 seconds or 5 minutes.
It is not semantics to say such. When the words STOP and GET OFF ME (or some derivative therefor) are not used...and there is no act of trying to get him off (of the girl)...then those words can mean several things...1) I don't want to do this anymore or 2) Hurry up and finish I have to go. Considering the girl consented...any 17 year old boy would think the latter. To think otherwise is denying reality.