https://canvas.fediverse.events/

It doesn't matter whether you place 1 pixel every 30 seconds or 6 every 3 minutes. One thing to keep in mind tho is that the 30 second timer seems to reset every time you place a pixel. For example, if you're at 0 pixels, gain 1, wait 15 seconds, and then place it, you'll still have to wait another 30 seconds for the next pixel. Meaning you basically lost 15 seconds. So I think the most efficient strategy is to place all 6 pixels as soon as you gain the 6th one.