The index cards will also teach you something.

Mix some 5-minute on the top card of the stack. When it's cured, peel it off. Didn't penetrate enough to stick did it.

Now mix some 15-minute. Won't peel off will it.

Now mix some 30-minute. Sticks the top card to the next one.

BTW, a box of toothpicks sits next to the stack of cards. They work for over half the epoxy jobs.
Also, a stack of 2-ounce "drug" cups from the Drug Store costs a couple of dollars. They're marked like measuring cups. Great for doing Epoxy Surfacing Resin mixes. The last sleeve of them I bought a couple of years ago still has a few left in it.