If you don't have a very reliable "get back to" system, you will feel each interruption has to be handled immediately, to prevent it from falling through the cracks.

 

 

Use a specific and exclusive piece of paper (or a post-it) only for a "get back to" list. Have it right at hand, at your aside all the time. Each time someone visits you during a "tunnel mode", excuse yourself and feed the list.

 

 

People won't like to guess when you are or are not in a focus period. Signaling it may help, for example with creative systems simulating some kind of traffic lights, but that requires a lot of discipline to keep updated (and it's very easy to forget putting "green" again when done, so people will wonder whether that's what happened and interrupt you anyway). 

 

 

Besides, people get frustrated if they have to keep coming back trying to hit a "green" (and the check-visit itself can mean incremental pressure to you: each time counts as a 'NO' you are saying). It's much easier just having a good way to note the "I need to talk to you" request and get back to them later. The more you really get back to them, the more they will trust you and your system, and the more your own brain will trust it also, enabling higher and higher focus as the whole thing works increasingly smoothly.