陈上伟博士:
"如果做为关键人才在18个月之内更换单位，须重新按照规定程序审核"。

I would like to ask:
(1) 做为关键人才在18个月之内更换单位，须重新按照规定程序审核. If one is successful for a new 关键人才 visa, the residence period can be added together.
(2) What happens on visa type (关键人才) when changing the job after 18 months?
(3) What is the minimun time to keep 关键人才 visa for applying a permanent residence card.

Thank you!