The other alternative is you start dropping requirements/features to meet their timeline, ideally leaning towards those they probably consider less important, c

The other alternative is you start dropping requirements/features to meet their timeline, ideally leaning towards those they probably consider less important, creating the altered project for them. I’ve found doing so to be crucial especially for non-technical communications and when you jump a level (talking to a boss 2+ levels superior) Otherwise if they won’t budge on time and features and resources, all you can do is put it in writing that you expect x-y time, and optimistically z might be possible. Ultimately half the manager’s job is to account for that uncertainty with buffers, and they’ll probably double it anyways before presenting it upwards/outwards. If they don’t add their own buffer… they’ll probably run into trouble anyways