Licensing & payments · The free trial
When does the free trial start counting down?
Short answer: It starts when you finish registering on first launch, not at download or install, and then counts calendar days whether or not the Mac is on.
The trial starts when you finish registering on first launch — after you enter your details and the email code checks out. Downloading or installing the app doesn't start it.
From then on it counts calendar days, so it keeps counting whether or not your Mac is switched on. The start and end dates are shown in Settings → License.