There can be only one primary task. When this happens, the question is, "what is worth what?" You must pose it to them, or others will ask for and expect both

There can be only one primary task. When this happens, the question is, "what is worth what?" You must pose it to them, or others will ask for and expect both. And where they lack knowledge, this must be escalated to someone who can make the call and account for said call; otherwise, you are already accountable for commitments made prior to their request. Doing both is not realistic, because there can only be one primary task, and this is why you end up doing work off hours. I would share more calendar details, put what the task is on the time block, and in general set up that question. Others will attempt to schedule your time so they do not end up doing catch up work off hours too. It is you or them, or something just is not as important as everyone thinks it is. Which is it? Also, make task switch time clear. A 30 minute meeting in the middle of, say a 2 to 3 hour block of time, may actually cost all or reduce the effective time to a small fraction of what is allocated. One effective way to handle this is to ask how many more meetings can now be scheduled into this wasted block of time? It can also mean moving that block slightly, allowing meetings at the very end of it, or before it starts. Either can be cheaper, with meetings at the end of it being cheapest generally. Your whole pushback is centered on there can be only one primary task. That is as real as it gets. Use it.