That's sneaky: introducing "je" without having taught it. Thank goodness for Wiktionary. https://en.wiktionary.org/wiki/je#Esperanto
It's in a Tips and Notes section, I think.
Ah. But those tips and notes are not visible on Android :-(
Edit: No, it was actually introduced in the first lesson of this skill.
Nah. At least not in Tips and Notes for Time. I haven't seen it in any of the Tips sections up to this point yet that I can recall.
Kial gxi estas "Kioma"?