First of all, it will hurt immersion. How couldn't it? What sounds more medieval:

"Your lordship, we have vanquished the Saracens in the year of our Lord, 1105"
I believe that is a minor issue.

It's enough to say "Your lordship we have just vanquished the Saracens." I find it certainly more detriemental to immersion when moving from France to German takes you several years. Also, sieges that streched over years were rare. But if a turn was, say 3 months no campaign could cover even 100 years.
I agree that there probably are better solutions, but I also aknowledge the problem.