critical period

https://doi.org/10.1351/goldbook.10574
Specific time in the development of a biological system when it is particularly vulnerable to injury or misdirection.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 741 (https://doi.org/10.1515/pac-2015-1202)