Just to be clear, when Armory starts up is using auto-bitcoind, it does the following:

(1) Starts bitcoind, requests its sync state
(2) Waits for bitcoind to finished downloading the 15GB blockchain
(3) Builds/updates the Armory databases from the 15GB of blk*.dat files produced by bitcoind
(4) Checks the stored address histories in the DB and compares against wallet addresses
(4a) If there are no addresses needing to be rescanned, it simply loads the histories
(4b) If the histories are incomplete, or you had an unclean shutdown (histories were never written to DB) -- rescans the full Armory databases
(5) Switches the interface to "online mode" and displays the tx history.

If your bitcoin-qt/bitcoind is already synchronized, then step #2 is minimal effort.  Otherwise it can take 4-48 hours depending on your connection (but you know that part). 

If you have not run Armory before, it will have to build the databases from scratch the first time in #3, which will take 30-120 minutes (on most systems).  If the DB is already built, it only updates the latest blocks (like 10 sec).

Step #4 either takes 5 sec (if already sync'd), or 10-30 minutes if it needs a full rescan.   This step will get much faster on the next release. 

If you did not add any addresses, or you did but they were part of a new wallet, then it should only have to do step #4 once.  After that, it will startup in like 30 sec.   If you see alternative behavior, it's probably a bug.

*The one exception to all of the above is the occasional DB corruption where it automatically detects and rebuilds.  Yes, annoying.  But I don't have any other way until I reduce the DB corruption events.