The short answer
Service timing should combine manufacturer guidance with evidence from the individual watch. Changes in accuracy, power reserve, winding, function or moisture justify assessment; water-resistance testing is a separate recurring need for watches used in water.
Compare the decision
There is no single interval
Movement type, age, use, water exposure and manufacturer guidance all matter. A fixed rule applied to every watch can lead to unnecessary work or delayed attention.
Watch for evidence
Changes in accuracy, reduced power reserve, unusual winding, moisture, damaged seals or unreliable chronograph operation justify professional assessment. Stop using a watch if moisture appears inside the case.
Water resistance needs separate attention
Gaskets can age before a movement needs full service. If a watch is used in water, periodic pressure testing is a focused and useful check. Water-resistance ratings are not permanent guarantees.
Document the work
Keep invoices and replaced parts when returned. Clear service records support future care and can help a buyer understand what was done without relying on vague claims.
Buyer checklist
- Record accuracy and power reserve before assuming a problem
- Note changes in winding, crown or pusher feel
- Follow reference-specific manufacturer guidance
- Pressure-test separately when water use matters
- Choose qualified service for the movement and brand
- Keep invoices and returned parts when provided
- Stop using the watch immediately if moisture appears