I'm a senior manager, too, and while i broadly agree with @RhiWrites I think we all need to be a bit more flexible and also take into account that people in Grad schemes need to know how to read the room, as it were.
I would also expect you to take your full lunch break which is important to mental and physical health as well as maintaining an effective work force.
I cannot disagree with this at all. The question is: is lunch from 12-1pm without fail regardless? Or is it an hour give or take a few minutes that can be made up elsewhere with flexibility (for, say, tea breaks, smoke breaks, simply standing up and stretching occasionally).
In Germany if you work one minute over 6 hours and haven't shown that you took at least 30 minutes break your company is in the poop. So for those with time-management systems the trick is either not to work a second over 6 hours or else you're stuck there (people working 30 hours p/w, for example) for 30 minutes longer. Or to make sure you time your breaks carefully.
I'm lucky that I've only ever had one job where it was literally "everyone down tools now" on occasion. But on other occasion we worked 36 hours straight (but then, the military - while having great respect for downtime - dances to its own tune sometimes)
This terrible toxic culture of presenteeism being cited by so many here is bad for people. Now especially we must challenge these practices.
Is also spot on. up to now "flexibility" in a job usually means that the employee is flexible about hours worked and salary and the employer reaps the benefits. (excellent and good employers are available). But we also need to recognise that if we want all round flexibility and WFH to be much more accepted and acceptable, we have to agree that there are ways of doing things. It's all in the execution rather than the principle of the thing.
Hopefully OP will learn to recognise when she can "can you call me back" to her boss and when she should "yep, what do you need?". That comes with experience, and getting feedback from other people (like us)