This is especially problematic in early business when the team is small and manager act with same policy/process as when at BigCo.

In this case don't estimate the time to build a poorly defined $something - invert the problem to estimate the value of $somethig.

It's amazing how many of those managers asking for estimates push back when they have to put one out. With all the same reasoning that engineers have when estimating.

A good manager should start with the Value first and allocate time-budget that makes that Value payoff.