As product managers, we have to work with a lot of departments – engineering, qa, 
order admin, finance, shipping etc as part of creating the product and then putting that product into the market.
Doing all of this, involves choreographing and managing a lot of activities, so that the final dance that results meets the customer expectations.
Here is a common answer I get when I ask people to commit to a date when a task assigned to them will be completed by them – “I am not sure, I have a lot on my plate”. Great, you think I don’t have anything else to do?
Don’t accept this answer but counter it with the following – “OK, I understand you are very busy and you may need to get more information before you can commit to a completion date. But can you give me a date when you will get back to me with a firm completion date?” This way, you are asking them to commit to a date to a date. To this, people will usually give you an answer.
Then when you end the meeting minutes, assign the action item to the person to get back to you with a completion date. Hold them accountable to the entire team and not just to you. Yes, unexpected things will come up, they always do, but you cannot run a business without a head and a date for each task.
Software Product Manager by Gopal Shenoy 
The problem becomes exacerbated when the engineering department has multiple dependencies. Example, “I can give a firm date to you next Monday but you know what, I need to know what the end date of Project X is because that has ramifications on my end date”. In my opinion, complex projects with inter-related dependencies should try to first unweave this situation and then approach the firm-date issue. Otherwise the firm date will be just a date with a lot of post-facto reasons available for not meeting it.
Sincerely
Subrata