This part is clearly nonsense:

> According to the planner’s calculation, the journey would have taken 43 days to cover 1,500 Roman miles. To put that into a contemporary context: the same route by road today can be completed in 14 days (340 hours) on foot, or 16 hours by car (source in Spanish).

It would take 340 hours to walk, whether you do it today or in Roman times. Google maps is assuming you would walk for 24 hours a day, the planner is assuming you could walk for around 8.