Any Roth conversion is reportable on the tax return for the year in which the distribution being converted to Roth takes place. That's why the deadline do do a Roth conversion is the end of the calendar year if you want it to be reportable on that year's tax return. This is entirely independent of the deadline for making an IRA contribution. They are two separate transactions. The term "backdoor Roth" simply confuses people into thinking that they are some sort of combined transaction.
