As a result of the attacks on September 11, 2001 there are now extra safety regulations at Schiphol. In connection with these, all departing passengers are requested to be at Schiphol at least 3 hours before departure. On the monitors in the central hall behind your flight number is shown which counter you have to report. The check-in counters are located in the departure halls.
If you want to check in late, it’s possible that the counters will be already closed and then you’ll miss your flight. Costs arising from this have to be borne by you.