I was once told by an old, well-experienced peer, "Manage your Manager"! I did not know what he means during that time as it was an ironic statement.
In real world project implementation, particularly in small projects, managing your manager is a must, else you will just burn your budget without delivering. These project managers wants you to devote your time to them. That means 100% of your time, but if you do, they will ask you, what have you done?
Project managers do not care about people. They only care about completing the project on time without blowing the budget. If money is running out, they want the project to be done fast.
Managing your manager is telling them that you just want to engage yourself with the project only when required. You know better how and when you need to create your deliverables. You need to be able to tell them "No", with assurance to be able to complete the project on time.
Some project managers want you to demobilize temporarily from their project. This is alright, but you need to tell them, "I may not be available when you need me, I am already doing another project".
Some project managers tend to become micro-managers who wants to know every minute details of what your doing, tell them, "Go away, I know what I am doing!"
There are many types of project managers each of which requires specific methods in dealing with them.