Can I apply clear coat a week after the base coat

The concept is that the base coat not being cured will be soft enough for the solvents in the clear to allow the clear to adhere to it like Paulster2 explained. You might get away with sanding the cured color coat and applying the clear but the surface needs to be rough enough for the clear to stick. The gamble is if the surface is sanded too fine, then the clear won't stick, or if it does, it won't be durable. If too coarse, will the sanding scratches show through the clear? Why not sand the cured color base coat with the same grit paper you used for the primer, reapply the base coat to fill the scratches, and then the clear within 24 hours? The hope is that the new color layer will stick to the cured layer while filling in the sanding scratches. Study the directions from your paint manufacturer with respect to time between primer, color, and clear. You also need to pay attention to compatibility of the solvents/thinners used in each coat, so staying with the same paint manufacturer for the job can't hurt.