Layoff notice, what does the 60 days mean? - 23 weeks in

My employer announced that the site will close and gave us written notice. I do not know if I should start looking now or wait for severance news. Has anyone been through this?

Keep everything in writing and save the confirmation numbers. It made the follow-up calls so much easier.

I stayed for the retention bonus and looked for work on the side. It cushioned the gap.