As a rule, a CTE will NEVER improve performance. A CTE is essentially a disposable view. There are no additional statistics stored, no indexes, etc. It functions as a shorthand for a subquery. In my opinion they can be EASILY overused (I see a lot of overuse in code in my job).
Check the cupcakes at the minimum baking time. If the recommended baking time is 18-22 minutes, check them at 17 or 18 minutes (just a quick peek, make sure not to let too much heat out of the oven). If the tops are rounded and no long appear wet, they may be done.
1 After the cupcakes are baked, test with a toothpick, if it comes out clean, they are ready other another 2-3 minutes..  Take the cupcakes out from the oven, if you still feel the tops are crisp, you can cover the cupcakes with a damp cloth or a normal cloth for 10 minutes.