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 5 minute break in between to check again if the meeting is really happening.
Productive, that's possible! Just find an activity with the following property:
leaves you in a state of mind very conducive to meetings right after
read a novel
do a Sudoku
eat a light sandwich
And that's it.
I'm afraid work productivity is not a true possibility, because your manager is explicitly wasting your time. That ...
Most of the other answers doesn't take into account the update OP gave in their post, so I thought I'd throw in my 5c:
The problem: I cannot work normally when I know I will be interrupted any minute.
How to continue working normally?
Are there any tricks to concentrate and ignore this situation?
That problem is unsolvable. You are a human being. By ...
The meeting is delayed? Just don’t work then.
Look, you are en employee for a company. While interacting with co-workers requires human interaction, I have news for you…
These are not really “human” interactions. These are business interactions.
In your case, your business task is to do work at your workstation until you have to do something else. Like be ...
In general: Write your thoughts and questions down.
(With respect to the upcoming meeting topic, of course.)
What are your ideas?
What problems and potential pitfalls do you see?
What questions could be properly addressed to you?
What questions do you anticipate (addressed to you others) that you could answer???
Depending on your role, is there a quick ...
If I was told there was a meeting about to start shortly, then I would probably do some small tasks until the time the meeting is supposed to start. If there is still no meeting going on, then I would continue with small tasks until ten minutes pass by. Once it is ten minutes after the meeting was supposed to begin, I would probably start working on major ...
Just filter out the time from the message.
In fact you might as well filter out the complete message, since in your workplace "we have a meeting at 14:30" seems to mean "we may or may not have a meeting sometime today/this week/next year."
When you do finally get called to the meeting, don't feel bad about taking as long as you need to "close down" what ...
It may or may not be applicable in this particular case, but I've found it a lot less stressful to work for an indeterminate time if I know I'll be able to take a minute or so to ‘park’ the work before going off to something else.
Especially if it's a task that involves a lot of thought, or juggling a lot of mental state, knowing I can spend a minute ‘...
... what can I do from my side to cope with this problem. How [can I] continue working normally?
As your manager said, "Don't think about it, just continue working."
Are there any tricks to concentrate and ignore this standby situation?
Know by experience that this type of meeting is fluid, rather than in stone.
Know that it has nothing ...
I'm assuming that advising you "just go on working" won't have much effect. The best compromise might be to try and find short, low-attention jobs that you can do around meeting time so you can instantly break off when you're called to the meeting and it won't matter if your mind isn't totally on the job.
These might be mundane administrative or ...
Don't pay attention on all this meetings times at all. Since even management is so unprofessional, that they don't care, why should you?
Concentrate on your stuff and only when meeting actually comes, you come in.