How long DeoxIT® will last/protect, depends on many variables; environment, temperature ranges, etc.
We generally tell people to apply, then check every six months. If inspection looks good, keep checking every six months.
You will then be able to quantify the results.
As a rule;
If the application is in a pristine environment (clean room), it should last 10 years or more.
If under normal household environments, it should last 3-5 years.
Extreme conditions; high salt, humidity and/or pollution, check every six months.