I took Rick's and Steve's advice and found this site with a very good explanation of microwave wood drying by John Williams.
http://www3.sympatico.ca/3jdw8/microwavedrying.htm
However the screen on the door of the microwave was so dense I couldn't tell when the ZipLoc bag had ballooned up so I stopped the oven at one minute and that seemed about the right amount of time.
After this initial test to determine the length of time to zap the blanks I no longer used the bag.
I cut off the ends of the blanks so that the coating of latex paint I had previously applied did not mess up the process.
I then divided the 12 blanks into three groups of four and proceeded with the following procedure. The groups of four blanks provided the 5 minute cooling off period that John recommends in his article.
1. Weigh the blank and record the weight.
2. Zap the blank for 1 minute and weigh and record.
3. Repeat steps 1 & 2 for each of the other three blanks.
Repeat the 3 steps until no further decrease in weight.
PS: Use a glove - the blanks get hot!
About 12 hours later I took a 4 item sample of the nuked blanks and ran them thru the process again and there was no further decrease in weight.
Bottom line: John's system works!
PS: Use a glove - the blanks get hot!