I am drilling panes of glass. 1st piece took 5 minutes 2nd piece took 10 minutes 3rd piece took nearly 30 minutes. What do you suggest?

Our diamond hole saw performed very well on the 1st cut but not so well on the 2nd and 3rd cuts. This only means that the diamond abrasives were lost at the end of the 1st cut.
It is important to note that these diamond hole saws need to be used with effective water cooling.
If you do not use water or if you apply too much pressure, the tip of the hole saw will overheat. The electroplated bond will locally lose strength causing the diamond abrasives to separate.
If you have efficient cooling, 200-300 RPM speed, and mild tool pressure, you can cut 10-20 holes in glass depending on the glass thickness.
Some of our customers are able to drill 30 bottles with one bit.