The frequency with which you should change the strings on your bass pivots on a couple of factors.
How often do you use your bass?
If you use your bass three times a week, the strings will wear out quicker than if you used it once a week.
Where do you store it?
If you leave your bass out in the sun without a cover, the wood is going to affect it, dust will get to the strings and moisture will get to it. Try to keep it protected in a cool environment.
What sound do you want?
New strings give a brighter sound. Frequency-wise, the strings emit more high frequencies than older strings. If you want a brighter sound, you’re going to need to change your strings more frequently than other bassists.
My recommendation is to write down whenever you do any maintenance on your bass on a journal of some type. This will give you an idea of when you can expect your strings.