1. How do you pronounce "Shrek", the movie title?
2. Then come to Peter's on Saturday, 12 o'clock.
3. Then come to Peter's at 12 o'clock on Saturday.
(Is Sentence 2 grammatical? What about Sentence 3?)
#1 is fine.
#2 would be fine if you delete the comma and put "at" before "12."
#3 is fine.