The scanning of the blockchain (I've found) was very quick, too about an hour.
May I ask your disk I/O and CPU status? I can't exactly remember which, but, one was very high and the other had quite a noticeable amount of 'background noise' when I was doing it (It was probably the CPU that was very high).
When I loaded Armory it scanned and successfully scanned it. Right after that I imported my watch only wallet and then it had to re-scan which gave me 66 months and did not change its status after about 4 hours. I closed and reopened Armory, and then the percentage went quickly to 99% then it was still scanning and the approximate time left programmed into Armory said 8 minutes, then two minutes later it went up to an hour. Do I have to re-scan the blockchain everytime I import a watch only wallet?
Unfortunately, I'm not one hundred percent sure, but, I'm pretty sure you do. It has to gather all transaction data it didn't keep about the wallet you just imported.