When did he learn about the dream zanakand and how to travel their.
If they learnt on their pilgrimage then surly Jecht must of learnt aswel and known he could return to the Dream Zanakand rather than becoming the Final Aeon
He did, but he choose to become the final aeon. When he did, he killed Yuna’s father, but it resulted in a "calm".
Ten years passed between Yuna’s father’s pilgrimage and Yuna’s pilgrimage.