vlad9 - Bitcoin network difficulty changes occur approximately every 2016 blocks, which translates to roughly every two weeks. This adjustment period ensures that blocks are mined at an average rate of one every 10 minutes, regardless of fluctuations in the network's hash rate. For more detailed information, you can check out this resource on Ultramining.com https://ultramining.com/en/btc-difficulty/ . It provides a comprehensive overview of how these adjustments work and their impact on the Bitcoin ecosystem.