Every app has its own clock
The trial is 15 days per app, counted from the day you first open that app. Opening Books today and Tasks next week gives you two trials that end on different days.
Autopay before the trial
Before a trial starts you authorise autopay — a ₹1 verification that is refunded. It lets the app carry on without a break when the trial ends. Nothing is charged during the trial.
Cancelling
Switch off autopay or end an app from Plans & Billing at any time. End it inside the trial and nothing is ever charged for it. End it later and you pay for the days used, never beyond the current period.
After the trial
The app keeps running and the days after the trial appear on the next monthly invoice. If autopay was switched off before the trial ended, the app locks until you start it again.