The maximum spacing between the blocks is 5 feet along the support board. A block is required under every joist so the spacing depends on your decking. The spacing could be 16" for 5/4 decking or 30" for 2x6 decking.
I don't know if you can answer a specific question like this, but what would you say the spacing for the blocks would need to be for a walkway that is 3' wide and approx 40' long? I assume I would I need 3 rows of blocks? I'm using a Trex decking material.