We can almost always say "it can't possibly take less than X". In fact, that X is often what gets given as the estimate, which is... not good, when you think about it.
We can also often say "it is very unlikely to take more than Y". Between X and Y is the range of possible values for a real estimate.
The problem comes when X and Y aren't just far apart, they're orders of magnitude apart. If you go back to your stakeholders with that range, what you should be able to hope for is a reasoned discussion not about how Y is too big (which it almost certainly will be) but on how to reduce the size of the range.
That involves having more information about either the problem or the solution, so you (or they) are either off into more analysis, or you're into solution design. When you have a design in terms of subparts similar to things that have been built before, you've got something that's less Sydney Opera House and more Sydney Opera House LEGO Creator Expert Set 10234.
So yes, at the specific point in time where someone asks you "how long to do this thing that's never been done before" there's almost certainly not enough information to give a response that bears relation to reality, but that should be the start of the conversation, not the end.
We can almost always say "it can't possibly take less than X". In fact, that X is often what gets given as the estimate, which is... not good, when you think about it.
We can also often say "it is very unlikely to take more than Y". Between X and Y is the range of possible values for a real estimate.
The problem comes when X and Y aren't just far apart, they're orders of magnitude apart. If you go back to your stakeholders with that range, what you should be able to hope for is a reasoned discussion not about how Y is too big (which it almost certainly will be) but on how to reduce the size of the range.
That involves having more information about either the problem or the solution, so you (or they) are either off into more analysis, or you're into solution design. When you have a design in terms of subparts similar to things that have been built before, you've got something that's less Sydney Opera House and more Sydney Opera House LEGO Creator Expert Set 10234.
So yes, at the specific point in time where someone asks you "how long to do this thing that's never been done before" there's almost certainly not enough information to give a response that bears relation to reality, but that should be the start of the conversation, not the end.