I have a Germany Blue Card and want to change my employer. And there is a rule in blue card:

> For the first two years of employment, approval from the Foreigners’
> Registration Office must be obtained before any change of job.

My current job contract is since 01.04.2018. Am I allowed to change my employer from 01.04.2020 without approval? Can I just sign a contract that starts on 01.04.2020? I have a blue card visa on my pasaport and also as a card with different dates, does it tied to them? 

I cannot ask to the authorities because they are closed.