You can easily spend several hours doing this, especially if you shoot with a friend. During this time you will find a marked change in the light on the target. Combining this with variations in the range and light conditions from your firing line will give you a lot of invaluable practice for the trailwalk. If you have access to uneven ground, you can set it up so that you can vary the angle to the target. Make sure that you have a safe backdrop.
Nobody wants a rifle ball as a surprise visitor.
I should also mention here that shot-up cans go to a recycling center. Some of the metal posts that hold up my fences once may have been the cans I shot. Fasten your next target upon it. The backer, coupled with its distance from the block, will keep your target from being ripped up by wood chips back-spattered from the impact of the rifle balls. Tape or staple a piece of butcher paper to the cardboard.