It depends on the length of the paper, the quality of the writing, and if there is an error near the beginning. Mochizuki's ABC papers had problems near the beg

It depends on the length of the paper, the quality of the writing, and if there is an error near the beginning. Mochizuki's ABC papers had problems near the beginning so that's why at least some problems were found rather quickly, and it also went "viral" in the community so more people looked at it. However, if this proof is sound, well-written, and is being looked at publicly by the top number theorists then it could be validated in under a year. Actually that's pretty much the same time it takes to peer-review a lot of ten page papers too that are not in the news...