* Who is surveyed: Parents, teachers, students, administrators, and the general public will likely have different perspectives. Parents of young children might favor shorter days for younger kids, while high school parents might prefer longer days for more rigorous academics. Teachers might have opinions influenced by workload and preparation time.
* What constitutes "shorter": Are we talking about shorter school days, shorter school weeks, or shorter school years? Each of these will have different levels of support.
* Geographic location: Cultural norms and educational systems differ across countries and even within regions of a single country.
* Specific proposals: The level of support will depend on the details of any proposed change. A proposal to reduce homework might have different support than a proposal to cut extracurricular activities.
To find data on this, you'd need to look at specific polls and surveys conducted in particular locations, focusing on specific proposals for changes to the school calendar. You will likely find a range of opinions, with no single definitive percentage representing global or even national sentiment.