I found a wiki article stating that Esperanto has an essive case, but not much of an explanation. Is the essive case in Esperanto basically an -e ending at the end of a word denoting a vague statement of the time ? This is the only thing I can think of in Esperanto that might constitute an essive case:
Vendrede - on friday
Parolante - while speaking
Semajne - weekly
If this isn't what would explain the essive case in Esperanto, what would?
And here is the source: