When Jack departed with the Themisphere, Aurebor, and Verremor's armies from Lorethion, his human age reached 22 months. His Limitless Potential increased to rank 14. At this rank, the race skill gave him HP +4500, Stamina and MP +390, and all attributes except luck +14.
It would take them several days to cross the Shylvan region. The armies marching from Hydrurond should arrive at Liguritudum's border before they did but they shouldn't be that far behind. Though those armies departed much earlier, those armies spent time building a supply line.
As for them, their marching speed was not slow due to two factors. Firstly, Jack's Runestone of Marching boosted the entire army's marching speed. Secondly, all the siege weapons were placed inside the mobile fortress, thus these slow-moving engines didn't slow the army.
Jack spent most of the time inside the mobile fortress during the march. He trained his mana manipulation during his free time.