Of course, it is impossible (and not desirable) to achieve 100% of productive time. There will always be team meetings, individual meetings between an employee and his manager, employees that go on vacation or have training.
However, in order to ensure that non-productive time does not take on excessive proportions, employees have to respect a certain ratio. In parallel, reducing periods of inactivity, "administrative tasks" and "other" would be optimal.
It is therefore useful to set a target rate for productive time, for example: 80% of employee time. For example, for resources working on billable projects, 80% of their time must be spent on billable activities related to these projects, with the remaining 20% devoted to administrative or operational activities.
If this goal is not achieved, it is crucial to investigate the root causes and identify proactive solutions to avoid making the same mistakes over and over again.
For example, you could ask yourself: