Some folks will use Ester with R12 because folk lore has it that it is "compatible" with R12. You are better off using mineral oil with R12.

Taking the test in an hour is pretty good. If you will print out the study guide, read it and then have it on hand when you take the test, you can probably get done in an hour.

The test is not laid out such that you can just go straight to the answer. Read the material first is my suggestion.

Good luck,