When a node-runner registers as a validator, they may set their validator fee % to anything they like - 0 to 100%. This will take effect at the start of the next epoch, when the network first considers the node as a validator for inclusion in the "top 100" validator set.
After this, validator node-runners may submit a change of validator fee % at any time. If the new fee is lower than the previous, it takes effect at the next epoch. If it is higher than the last, a delay is applied in epoch time, equalling 4,032 epochs, approximately 2 weeks. The new higher fee will be visible on the Radix Dashboard and to current delegators, i.e. Liquid Stake Unit (LSU) holders, during this time. Delegators will continue to be credited with emissions based on the previous fee while deciding if they would like to remain staked.
Further reading:
- What are validator fees?
- How XRD staking emissions rewards and validator fees are calculated - for validators
- How do I run a validator on Radix?
- What is a validator component?