The brushing frequency is up to you, but the more time you wait the greater the chance of uneven development. This might only be a problem with some staining developers like ABC or PMK.
If you are seeing good results with your technique then dont worry about it, the main idea of brush development is to obtain the most even negative possible.

In my case I keep a continuing motion, I start at the top, brush down and then bring the brush to the top without brushing, move it about an inch to the side and brush down again.