No. 理論上你隻有0天時間來轉身份 according to lawyer

But the day is start from you are off payroll. In CA, lay off 50+ employee request 2 month notice. So you may lost job, but you still in payroll for two month. You are still good. The package (n weeks/pre year, can be 0) is compnay good will. You need ask when is your last payroll day. You are still in H1B as long as you are in payroll. If you find a new job and you can do a H1 transfer. as long as you filed the H1 transfer, you can working for new company. You can have multi H1 and workign for multi company.
p.s. For H1, Your company is response for the one way ticket to send you home country.