One of the duties of the referee enumerated in Law 5 is the filing of a match report. Our leagues mandate, as a condition of being paid, that game reports be filed within 48 hours of the assigned game start time. For example, if you are assigned to be the center referee on a game that starts at 9:00 AM on Saturday, your game report must be filed no later than 9:00 AM on Monday morning. Arbiter time stamps your report and the leagues check for late reports.
Report filing only affects the center referee. Assistant referees do not have to file a report and are always paid regardless of what the center referee does.
A referee best practice is to use your smart phone or tablet to file the report from the field or to complete it as soon as you arrive home on the day of the game. Referees who wait often forget to file the report.