Here is a summary of the various appointments and meetings scheduled among the characters in this story, sorted by date and time:

1. November 28, 9 AM: Samantha and Peter will meet at Caroline's Cafe for their AI project discussion (planned by Samantha).

2. November 28, 1 PM: Leo and Diego will have a meeting under the oak tree to continue discussing AI projects (proposed by Diego).

3. November 28, 3 PM: Peter, Andy, Noor, and possibly others will meet at Caroline's Cafe for their AI music project discussion (proposed by Andy).

4. Unspecified date before December 4: Leo and Peter will have a coffee date under the oak tree to discuss Peter's solo gallery show aspirations (planned by Peter).

5. December 4, time unspecified: Samantha and Mei will meet at Caroline's Cafe for their AI project discussion (planned by Samantha).

6. December 4, possibly the same day as #5: Leo and Diego will have a meeting under the oak tree to continue discussing AI projects (date proposed by Diego during their November 28 lunch meeting).