Ascension works through collecting ascension points. Each turn you hold one ascension crystal, gives one point. If I recall correctly, you need (the insane) 1000 points to actually win. That means that if you have one crystal, you need to wait 1000 turns ("weeks") before your ascension is complete. If you hold two, you "only" need 500 turns. If you hold all 5, it still takes 200 turns to win the game through ascension. So basically, the Iconians may have gotten a crystal first, but because the Drengin have gotten themselves two, they will still finish ahead of the Iconians, even though they may have fewer points right now.
Ascension really isn't a problem though. As I said before, even when holding all 5 crystals, it takes a whopping 200 turns. If a race is strong enough to hold all 5 bases for 200 turns in a row, it might aswell have gone for a conquest victory (it would've been won much easier).