Wery good analysis my friend !!!
Actualy "when IT will arive" means attainment of stream entry (because OP ask about how to know if some one is stream enterer). Also "IT" means this "powerfull insight" , because this insight (whitch is personal to each practitioner, like a different key openes different door) brings you a clear vision of anicca, dukkha and anatta (or just one of them) in all obsevables phenomenas.
This insight can arrive when you eat, when you walk, when you just seat, in jhana too etc. All depends on "readyness" of fruit. And when it falls you cant miss it because its change you from the deep. All depends on one's purity of mind, some beings just on hearing about anicca, dukkha and anatta for the first time attein Arahanship, others nothing at all... So when fruit is ready, it falls.
What about joy, its about Laughting Buddha, when you realise that somethink is just a joke - you laught, when you realise and sees that somethink that you was affraid is illusion you laught, feel joy, you wana to go out and scream to everybody - " Wake up!!! Its just an illusion !!! Dont be affraid!! " but you cant because there is difference between conceptual and direct understanding of things, if someones mind is ready - he will realise it by founding his own key (satipatthana is about searching the key, samathi is about seeing him), if someones mind is not ready - you can tell him all about Dhamma, read him all suttas, tell him that all is anicca, dukkha and anatta many times, but he will say just - "yes i know, and what? ..."
Actualy its no metter how it heppens and how you feel it, what is important is uprooting of fetters.