Or roughly every 136 years.

How so?

See for yourself

> date -d '@1600000000'

> date -d '@1700000000'

1 year are 31557600 seconds so roughly a third of 100 million seconds 1.7 billion seconds since the epoch is the next big rollover since 2020 and the 5th-last before 31 bits are not enough to hold the seconds since the epoch.