She might have been pregnant even before Manalo Conference start.Timeline becomes confusing since based on the baby's appearance, it's clearly about more than 3-month old. And then couple it with the 9-month pregnancy...
Over a year has a passed since Kukui and Burnett got married. At. Best. If she got pregnant shortly after Ash left, then Ash has been gone from Alola at least a year.
Wait, how could Journeys be somehow longer than the OS-SM series combined?