Layoff notice, what does the 60 days mean? - 18 weeks in

Our team was told about a closure date that is 18 weeks away. I am in Denver, in case local advice matters. I do not know if I should start looking now or wait for severance news. Has anyone been through this?

Thanks for writing this out. I went through something close to it 11 months ago, and it got easier once I kept a simple log of every call and form.