Tier 2 ICT to ICT dependent to Tier 2 General

Hi Team
Need your advice on my scenario. I am tier 2 ICT visa till October 2020. My wife is on her Tier 2 ICT visa till February 2020. I am planning to go on her dependent and then look for Tier 2 General Sponsorship. As far as I know, I have to work in ICT dependent for at least 12 months and then I can look for Tier 2 General sponsorship but for that I have to apply for it outside UK. Can someone please advice on this? Is my understanding correct? I don’t have to serve a fresh 12 month cooling off from Dependent to General? And working on dependent for 12 months is mandatory?

As far as I know, I have to work in ICT dependent for at least 12 months and then I can look for Tier 2 General sponsorship but for that I have to apply for it outside UK. Can someone please advice on this? Is my understanding correct?

Correct.

I don’t have to serve a fresh 12 month cooling off from Dependent to General?

No.

And working on dependent for 12 months is mandatory?

Working is not mandatory no. You simply need to be on any other visa other than a main ICT visa.