My cat can watch squirrel videos for half an hour. I find it works well when the tablet is vertical, not flat on the ground. He play with the progress bar as well (probably not intentional, but he did manage to fastforward until the squirrel came back in the screen again).

Every time I go through a unit (20 lbs) of cat litter, I dump the litter, clean and bleach the box, and rinse the hell out of it. Then, I place new litter. I'd say, approximately once ever 1.5 months.