Still learning

Definitely first thing in the morning!

Also, keep in mind that those strips are not reliable long term. They aren’t known to be finicky. If you want a 100% accurate reading. Then I would suggest buying a test kit that reads your blood. It’s just like a glucose monitor except the strips are for Ketosis. You can find them at GNC. They’re around 50$ and the test strips are about 15. 

ledonne.tammy Agree on the unreliability of the paper - "pee pee" ketone strips. They are sensitive to light and humidity, so keeping them in the bathroom long term isn't always ideal. Having said that, I usually use them first thing in the morning, too. 

The benefit of the blood ketone monitor, however, is that measures the ketones in your blood, which is more accurate than your urine. Moreover, there are a lot of people who will test their ketone level right after they eat a meal to see how their body reacted. This can be super useful when you're tweaking your diet. For example, some artificial sweeteners may say 0 net grams of carbs, but they have a not so Keto glycemic index. Getting that data in real-time can save you a real headache in figuring out why your weight loss has stalled.

Interestingly, the longer your body has been in ketosis, the more fat-adapted it will become (adapted to burning fat, that is). The consequence is that your body will become more efficient at using ketones. So often times, when you've been in ketosis for a while, your urine strips might not reflect it. It may actually look like your ketone level has gone down. This is because your body isn't producing them and wasting them, it's actually transforming into a super efficient machine!