What if I wanted to say his cousin arrived on the tenth? Like tenth of May. Wouldnt i use je for that, too? En doesnt feel right.
Tio okazis la dekan. = Tio okazis en la deka tago de la monato.
Tio okazis je la deka. = Tio okazis je la deka horo de la tago.
"ĉe" is only used for someone/something's location in space, not time. Also, "dek" is only used for the number, rather than the time.
Apud = beside Cxe = at Je = that preposition that is used when no other preposition exists that can accurately conveybthe meaning
Je is used to replace another preposition, but what preposition does it replace here?
Je is used when we know there should be a preposition, but aren't quite sure what preposition to use, or when there isn't a specific preposition for it.