The whole Bittul Torah argument is irrelvent. Everything is Bittul Torah unless its Torah
Even Eating, Sleeping and going to the Bathroom is Bittul Torah .
How many stories have we heard of great Rabbanim who slept only a few hours a night so they could get every last minute of learning in.
If you are able to spent every moment you have learning, Kov HaKavod. Most of us cant and need breaks.
Healthy Breaks can actually make one learn better as you get refreshed.