As far as I know, the Church has never declared watching too much tv to be a “sin,” nor sleeping too much, reading too much or walking too much. Certainly, your time could be better spent but what makes you think it is a sin? There is enough sin to go around; stop looking for it where it isn’t.
Sloth is not just a sin but a deadly sin - and not just spiritual sloth but any sloth. MInd you the OP IS talking about spiritual sloth - spending too much time on other things and as a result not devoting time to prayer as they ought.
Sloth means laziness, a disinclination to work. How do you define sloth, then, if not spending excessive time on watching tv or sleeping too much? You’re wasting time and not working as you ought. Be it time that you should spend on prayer, or time you should spend on your work, or time you should devote to your family and friends, to doing works of mercy etc.
Your time is to be spent on God’s purposes, not just your own recreation. A moderate amount of tv or sleep is OK, too much isn’t godly. Why else would diligence be a virtue if significant failure to be diligent wasn’t a sin?
Proverbs 6:
"6 Go to the ant, O sluggard,
Observe her ways and be wise,
7 Which, having no chief,
Officer or ruler,
8 Prepares her food in the summer
And gathers her provision in the harvest.
9 How long will you lie down, O sluggard?
When will you arise from your sleep?
10 “A little sleep, a little slumber,
A little folding of the hands to rest”—
11 Your poverty will come in like a vagabond
And your need like an armed man. "
The other activities are just that, activities. You’re not slothful if you’re doing things (unless you’re, say, skipping work to do something less important like clean house), and reading or walking = doing things. Watching tv and sleeping = doing nothing.