The search for the Grail prior to the final battle must had taken 5-10 years. The Western Roman Empire lost it's hold on Britain at about 430 AD. So you have a 100 year span between that event and the Final battle between Arhur and Mordred. I would estimate 30 years realistically. Of course, in Type-moon's scene, you can extend it to 100, and it would be plausible.
__________________
Into terror!, Into valour!
Charge ahead! No! Never turn
Yes, it's into the fire we fly
And the devil will burn!
- Scarlett Pimpernell
__________________
Into terror!, Into valour!
Charge ahead! No! Never turn
Yes, it's into the fire we fly
And the devil will burn!
- Scarlett Pimpernell