It depends how you are updating the grid on which your agents are stored. If, after an agent moves, you are telling that agent to update its location in the grid, then when the next agent queries the grid it will reflect that other agent's new location. If, however, you are not updating the grid until all agents have acted, then the new locations will not be accessible until the next time step.
In netlogo terms, you can think of it as:
ask agents [
ask agents [ do-stuff ]
ask agents [move]
MASON does exactly what you tell it to do, when you tell it to do it. Not all objects are thread-safe though, so if you're updating something across multiple threads, you may want to synchronize your actions.