The Pomodoro Technique
Might be a practical way to deal with this, at least a modified version.
Perhaps slightly before meetings are scheduled, break up whatever you're working on into very small very achievable mini-goals and give yourself 15 mins to work on each one with a five5 minute break in between to check again if the meeting is really happening.
That means you should be able to get 3 of these done per hour, and get some stuff done even if the meeting is delayed for a really long time, like over an hour as in your example. It also means that you're either working or asking whether the meeting is happening, not both simultaneously, which should help you to actually concentrate during the pomodoros (pomodori?).
Tell yourself that a pomodoro is either going to be done, or not done. Simple. If you get summoned in the middle of one, think of it as 'burned', and then after the meeting have one final pomodoro where you start the interrupted one over from scratch. Maybe literally, as in you delete the work you did in the previous one and start over, so you don't have to waste energyif picking up the thread where you left off would take more effort. This means that at most, 15 minutes of your work and concentration will be wasted by this, which might be a little less frustrating.