In the U.S. the WARN act does mandate 60 day notice for layoffs over a certain size. In practice, (at least with many of the recent tech layoffs) you get 60 days on-payroll during which you don’t have to do any work. Severance after that is optional but often still paid, again at least among tech companies. ~2 weeks per year of service is common, although some have offered more than that.