General:
* Lost time
* Idle time
* Dead time
* Unproductive time
* Time spent in vain
* Time frittered away
* Time squandered
More specific:
* Procrastination: Time spent delaying or avoiding a task.
* Distraction: Time spent on things that take you away from your goal.
* Indecision: Time spent struggling to make a choice.
* Mismanagement: Time lost due to poor planning or organization.
* Boredom: Time spent feeling uninterested or unengaged.
* Downtime: Time spent relaxing or not working, which can be useful or wasteful depending on the situation.
The best word to use will depend on the specific situation and what you want to emphasize.