How do not disturb day can improve your productivity?

One of my previous jobs was at this company which was very inefficient with people's time. Everyone had access to everyone elses calendar and they'd keep booking your time in meetings so your calendar ended up like Swiss cheese - lots of 30 minute holes that were absolutely inadequate for getting any work done.

What I started to do was doing what this article mentions, but just for me - blocking out 2hr meetings every other day "with myself" in my calendar weeks in advance just so I can have a dedicated time to work.