Here is a complete timeline of all events that take place in When Worlds Collide.
| Date (MSC) | Planet/Earth (Earth IDs) | Description |
|---|---|---|
| January 19, 0 | All of them, including Non-Earths | The Great Merge occurs |
| February 2, 2 | Great Detroit (E-III) | Groundhog Day Massacre; Stimpson Cat dies. |
| February 6, 2 | Great Detroit (E-III) | The Reich Resistance forms. |
| March 11, 5 | Wolfenstein (E-I) ; Danville (E-II) | Wolfenstein invades Danville successfully; Dr. Heinz Doofenshmirtz dies. |
| July 4, 6 | Danville (E-II) | The Danville Resistance forms. |
| September 1, 7 | Danville (E-II); Great Detroit (E-III) | The Allied Resistance forms. |
| July 17, 8 | Great Detroit (E-III) | Ren Höek dies from old age. |
| August 4, 9 | Wolfenstein (E-I) ; Atoll | Atoll is invaded by Wolfenstein. |
| September 3, 10 | Danville (E-II) | ICENE forms. |