First, I would not use the external zip as a source drive. It's interface is either USB1.1, serial, or parallel port and those interfaces are too slow to supply constant data to your CD-RW drive. I would suggest copying the data from your zip drive to your hard drive and then burn the data from the hard drive. This will cause the burning process to be faster than your current rate. Additional RAM could also help boost your burning times. As for your question about how long a burner can stay in record mode without damaging the drive , I don't really know if there is an answer to question. I've burned 40 CD's in a row before with no problems with my drive, but the drive did get hot after so many burnings. I would also make sure your computer has proper cooling.