That's up to you. My snake are adults and may go 6-8 weeks without making a mess. Sometimes they may go much more frequently.
The main thing that works for me right now is to spot clean VERY liberally when there is a mess. If I see urates the size of a quarter or less, I clean about a 6-8 " circle or beyond what I see that is obviously wet. If there are urates about the size of my palm, I will easily clean a 12 " circle or more if I still see wetness.
Then, after 2-3 spot cleans or splashed water I change it all out.