Measure it yourself
Measure twice and cut once sounds great, but it usually runs against the more realistic perfect is the enemy of good. However, you should never jump to the other extreme not measuring — or what is almost the same: trusting the measurements provided by others.
I was reminded of this by the new Screen Time in iOS 12. As an impatient fanboi, I enabled a daily 1 hour allowance on my Social Network group apps as soon as I upgraded my iPhone. I started hitting the limit on Tweetbot, Amaroq and Instagram right away, but I trusted it was measuring the right thing.
The fail became evident today when in a middle of a work call, Skype reached the Social Network limit.
I lost 1 week of behavior data which I could have used to apply representative limits per apps. A borderline banal problem in the real world, but an actual lesson to self when looking at fast implementations of any software/system.