Update rate of commands

[axiomofdarkness]

How often is the "Execute" method run on commands in command-based? We are trying to do something which relies on sensor and motor controller values being updated at a constant rate. I am worried that these methods will be called at irregular intervals. So if there is a set rate at which they are called, what is it? And if they are called irregularly, how might I go about ensuring that this information is updated at a regular rate? We are using C++, if it matters.