What do these preposition expressions mean?

[elsa]

Hello, please I need your help. I have some doubts about the use of the prepositions ON/IN/AT and I want to know the accurate choice for these sentences:

We want to start the meeting on time/in time, so please don t be late.
Where is the car waiting? At/on the traffic lights.
The leaves on/at that tree are a beautiful color.
He spends most of the day sitting at/on the window and looking outside.
I like that picture hanging on the wall in/at the kitchen.

Thanks a lot.

[luvma1s]

the first sentence, i choose on time
the second, i choose at
the third, i choose on
the fourth, i choose at
the last sentence, i choose in

i don't know if the answer is correct but i hope so

[elsa]

Thanks for your reply. What do you think about these ones?

I saw Ana at/on Dave s wedding.
He goes to classes at/in the university.

[Andreana]

I would say 'I saw Ana at Dave's wedding.' and 'He goes to classes at university'.

I saw Ana at/on Dave s wedding.
He goes to classes at/in the university.

[elsa]

Thank you Andreana