This is a conjectural timeline for Grease 2. The Rydell School year would have been 9 months, starting 9-4-1961 and ended 6-15-1962 - ignore the incorrect dates on the June Moon Talent Show's Calendar Girls set pieces.
9-4-61, Monday. Back To School Again and the first day. September First 1961 was a Friday, so up that to Monday the 4th.
9-12-61, Tuesday. The scene at the track / Score Tonight, Steph kisses Michael.
9-25-61, Monday. Talent Show Rehearsals / Try-Outs. Mrs. McGee said on PA during the first day of class that the rehearsals for the Talent Show would begin `next month' (October). They might have put the try-outs for the talent show earlier than October, maybe on the urgings of Stacie & Gracie. Ms. Mason seemed to get along with them the most, so perhaps 2 weeks after `Score Tonight'. That might make sense; Michael didn't see Steph for a couple weeks before he saw her again at the try-outs, and asked her about why she kissed him - then got reamed with `Cool Rider (Song)'.
9-26 Louis' essay "How Rome Fell"
It might have taken Michael months to build his motorcycle, finding the parts. Then figure a couple months self-training (also helped with his `tough' image by Frenchy).
Still working this section out
6-14-62, Thursday. Final dress rehearsal for the talent show. Most likely this was when Michael and Steph were at the Burger Diner.
6-15-62, Friday, Charades / June Moon Talent Show / Lone Rider's disappearance.
6-16-62, Saturday. Lani Kai Lani Luau. Michael & Steph reunited
6-18-62, Monday, Graduation pictures