Albanian: length of time in the Balkans

Dear all, we know that there is no hard proof that Albanian is descended from Illyrian, but it would make sense in other ways. The fact that some Latin loan words are present in Albanian in heavily disguised form, does that add to the proof that the Albanians have been in the Balkans for a long time? I am thinking of words like njëqind, related to centum. Is there any linguistic proof of the length of time Albanians have been in the Balkans? I suppose everyone knows that many Serbs argue that they came to the Balkans only in the 11th century, and they also try to argue for a connection between Albania and the (unrelated) Kingdom of Albania in the Caucasus. I think linguistics could shed some light on the surprising emergence of Albanians in the 11th century after many centuries during which the Illyrians were not mentioned.