currently we have a client that have a series of requirements (very broad and general) for an app. I as the PM was asked by my boss to estimate how much hours of work were required to make that app. Now, given the requirements I can see this taking between two and two and a half months, but since this estimated hours are going to be use to charge the client I need to go into details to give a proper estimation.
The problem is that my boss want this ASAP, 1-2 two days (big surprise), but of course I'll need to review this carefully with my team in order to give a proper estimate, and there is always the posibility that the client don't like the proposal and declines the offer, therefore we will lose a lot of time. My question is how should I balance the time invested to make an estimation? How much minimun time should I invest? Should I talk to my boss and explained to him why I need more time? Or should I give my glanced estimations of two and a half months?
I write down the requirements and transform them into user stories, etc, but since we need to work with a third party we do not know for sure how their system (ERP) works, that is the reason why I believe that a lot of unforeseen problems my arise.