Sure! Here’s the text filled in with the correct prepositions of time "at," "in," and "on":

I'm going to have a party! I hope you can come!!
It's going to start (1) **at** 5 o'clock (2) **in** the afternoon (3) **on** the
second Saturday (4) **in** August. We're going to have it in Tom's house on Wilton
Avenue. There's a big garden and we're going to have the party in the garden.
Did you know that my birthday is (5) **on** the eighth? But as you can see, the party
is going to be (6) **on** the tenth. Why? Parties are better (7) **on** the weekend!