They are good stand alone sentences.
We rarely use “a.m.” or “p.m.” in speech. “Saturday at 7” or “Saturday morning at 7” if not clear from context.
He was/is supposed to buy his ticket(s) in advance.
Also, the sentences are good by themselves, but they don’t fit together smoothly, if that’s the intention.
What are you doing this Saturday?
In the morning I’m going fishing on the river, but I have to clean my house in the afternoon. Later, at 8, I have to take my father to the train station. Which reminds me, he’s supposed to buy his ticket in advance. I better send him a text so he doesn’t forget.