In most cases it's 12 months.
If a PI has funding from an institution that requires the paper to be immediately available via a Creative Commons CC BY license (NIH does not require this at this time), there is no post-publication embargo period. Per Science:
"Authors of peer-reviewed research submitted to a Science subscription journal on or after 1 January 2023 who are required by their employer or funder to distribute their accepted manuscript under a CC BY license may do so upon publication of the final version by AAAS"