Touring and active players may change every few days or weeks. Others go months, and some intentionally keep strings on for years because they like the broken-in tone. String life depends on how often you play, your playing style, body chemistry, environment and string type.
Bass players often leave strings on longer than guitar players, since bass strings are heavier, vibrate at lower frequencies and many bassists like the warmer sound that develops as they break in.
Construction matters too. Flatwounds change more gradually and don't collect contamination as easily, so many players leave them on a long time. Semi-flats also develop their tone more gradually than roundwounds.
Broken-in isn't the same as worn out. Replace strings that are corroded, damaged, hard to tune or intonate, or have lost too much definition. Changing strings is one of the most affordable ways to refresh your bass's sound.