A ball is lost if not found within three minutes after you or your caddie begins searching.
Plain-language guide · Rule 18.2a. Use the current official text and your round’s Local Rules for a ruling.
What to know
If found near the time limit, reasonable time is allowed to reach and identify it.
On the course
Start a timer and look in the likely area. If the ball is lost outside a penalty area, use the proper lost-ball procedure.