2) Yes if asked.
3) Depends on the company/customer/PM.
I'm coming from the perspective of a software developer in the automotive sector. The jobs I'm assigned to are often under-quoted on hours for any particular task, and even if they're not under-quoted, the final date before project completion generally can't move, so any slips in previous departments tend to end up in my court for resolving (Robot/NC/PLC programming are usually the final stages of a given project).
The PM is hired by the company to forecast resource allocations for any particular project as s/he sees fit. This means, in general, that the forecast will never be 100% accurate. However frustrating this may be, there are several solutions that don't involve getting upset with the PM and demanding that they at leas consult the dev doing the work before forecasting (trust me, it didn't work for me, and it caused a large number of issues for me professionally). The PM may also feel that an attempt to tell them they're wrong is a slight against them professionally or personally.
The best way to approach this IMO (and I'm answering the question I feel is implied at this point) is to cover your back and document everything. Keep a detailed list of tasks, the priorities given for each (which the PM should be providing), how long each task took, and if it took longer than expected, a detailed reason why (be honest, even if it's your mistake).
In my particular company (Italian company operating in the USA) missed timing requires an NC (non-compliance) to be filed. This NC can be filed against any of a multitude of stages of the project, including the PM or proposals teams. If your company does not have such a procedure, keep a log of things that delayed your ability to complete tasks.
If the PM is supportive of it, I would also suggest putting out a regular report (daily/weekly/monthly depending on the project term and the perceived deficit of hours) keeping a log of what was tasked for that time period, versus what was achieved. The explanation of any resultant gap is in the documentation you should be doing to cover yourself.
TL;DR the PM is trusted by the company to do as they see fit for forecasting. The only thing you can do is request they prioritize your tasks, and document anything/everything that doesn't meet the timeline.