It is common in option modeling to differentiate between diffusion or volatility time, and the forward period for the underlying. The instant you execute an option trade you are exposed to price movements in the underlying even though a spot trade in the underlying made at the same time hasn’t yet settled. See where this is going? A settlement lag in the underlying may interact with its date roll convention such that the forward period may not coincide with the volatility exposure period. Any decent textbook should show this distinction.
The moment you trade the option you have to manage the risks in your book. The differences between trade and settlement usually are the same when you open and close your position so the number of days of the "carry" won´t change, just make sure to account for it.
The forward days and volatility period mismatch is exactly my point and I look everywhere but I haven´t found a way to deal with that.