I apologize that I can't tell you exactly when to convert in order to maximize the opportunity for rewards. However, the CSR travel credit is based on card member year, and no longer calendar, so it's no longer possible to get two travel credits in year 1. Good Luck.

Edit: Just realized you are doing a product change, so your account anniversary will be based on the CSP. When you convert, you'll have access to the $300.00 travel credit immediately. Chase should charge you the next annual fee on your 2024 account anniversary, but, when I converted a Marriott to a Ritz, it took them a little while to sync everything up.

It's possible you might be able to go 2 for 1 after all.