need help mostly with estonian grammar

hi to estonian natives/speakers.

i need help in some linguistic points of ranged difficulty such as:

when is the Subject of Present Passive Voice (-kse)/Past Passive Voice (-ti) in Nominative and when is it in Partitive?

or:

"mis ajal süüakse Eestis õhtust?": does this mean "when does one eat in Estonia?" "mis ajal?" means "when?" like "on what time?" and what does "õhtust" mean? is the latter in Elative and why if thats the case?

i d really appreciate it if someone could give me some answers. i m willing to get them one way or another, so it doesnt matter if you ve seen this post after a month or a year. feel free to contact me.