>>677279There really isn't any right time to check it since its all dependent on the amount of material, water flow and the angle of the sluice box.
That being said the heavier material will first collect in the upper segment of the box and later towards the bottom. You might want to clean out when the material piles down to where your not comfortable with it.
Also a nifty piece of equipment to invest in is an automatic panner. The Desert fox one is awesome because it recycles the water and can be run with just 2 gallons. You put your concentrates in it and it does a lot of the work.
