A timer for the session, not a ban on YouTube
There are plenty of reasons to use YouTube intentionally. A timer lets you keep that access while making it harder for an open-ended session to disappear into the recommendation loop.
When the timer is reached, Come To interrupts. You can stop, or consciously choose another interval instead of continuing without noticing.
Use a separate limit for video if you need one
Video sessions may deserve a different boundary from social feeds. Give YouTube its own timer, or group it with other video apps that should share the same active-use budget.
Timer profiles are independent, so the remaining time for your video timer does not have to match your social timer.
Time outside YouTube does not spend the YouTube timer
Come To is built around the active selected app. Switching away from YouTube to an unrelated app, returning home or locking the screen should not keep consuming that timer as if you were still watching.
That makes the reminder correspond more closely to the behavior you meant to limit.