[bbrunner]

Tell the product owner what the situation is and collaboratively come up with either:

a) a new timeline that you believe you can meet or b) a list of tradeoffs that can be made to get the project out the door in time

I have been an engineering lead and a product manager and it is much better for everyone to just be upfront about all of this.

You know what your team can produce and (roughly) how fast they can produce within an order of magnitude time-wise. The product owner should know what stakeholders actually want product-wise and what an acceptable timeline looks like. You should be able to work together to narrow the scope of what is being worked on to a point where your team can accomplish it within the timeframe.

Communication and setting expectations are key. This needs to be done both up front and on an on-going basis. As an engineering manager, you should be able to evaluate, week-to-week, where things stand and which tasks may need to be cut to make a deadline or how far a deadline should be pushed back if things can't be cut. Your product owner should be able to weigh in on this and should already be prepared to pare down requirements if necessary.

It may be painful and embarrassing to start having these conversations now, but it is significantly less painful and embarrassing than having these conversations in 3 months when the product is expected to be delivered.