Sometime after the 12th/13th cycle…
Ramza was a noble who originally enrolled in the Gariland Military Academy to come a knight of the Northern Sky. However, due to an eye opening revelation about classism, he becomes a mercenary. Later, Ramza entangles himself in a demonic conspiracy involving the Lucavi.
When does Materia call Ramza to World B? He could have arrived sometime after he returns from the Underworld.
Probably the most likely scenario is sometime before he comes a mercenary. When he arrives in World B, he’s still wearing his cadet clothing.
Before the disaster at Fort Ziekden, Ramza progresses through several excursions during his journey. It takes about a day to travel to each landmark; it’s possible he could have arrived in World B during one of his journeys. But he most likely wanders the world, after the death of Delita’s sister Tietra.
I had lived my life the only way that I had known. But when the pillars of that life came crashing down, I did not stand and watch them fall. I turned and walked away.