Adjudication taking long

I was given an estimate start date of March 15th for a new job. but because of my security clearance continue to be pending processing it’s not happening.
I was wondering How long the employer will wait before they withdraw my candidacy if the security clearance will continue to be pending in adjudication?

My first job wanted me to get a secret. After a year passed without a decision they decided to let me go. I’m currently waiting again at a new job almost 7 years later and I started there a year ago next week. Still no decision, so hopefully they hold on to me.