Normally, it would make sense to check it a year before the warranty runs out and then every couple of years afterward. That’s unless you soften. If you soften, it should be once a year.
The rule of thumb is to replace when there is six inches of exposed core wire.
Since you’re concerned about the glass lining, check in one year. If it’s mostly intact, check two years after that.
I learned the hard way that leaving it too long is a mistake because conditions can change. Water is a chemical that is constantly changing and sometimes that has an affect on water heater life.