My Benq 1650 takes, in average, 15-16 s to recognize a DVD from the moment when the tray is completely closed. Some discs even need 20 seconds to be recognized. CD's take few seconds less, but 5-6s longer than my Liteon CD-RW. Apart from that the drive reads discs normally. I don't know if it is normal and if it is a first sign of a malfunction that will develope in time.
How long does it take for your 1650/55 or 1640?