Tier 2 General extension

[Britishhope]

Hi,

My Tier 2 General Visa expires in August 2021.
My employer is planning to start the VISA extension process by April 2021(i will have 4 months validity left).
Is April is too early to apply for extension and get the CoS ?
i read somewhere we can start filing extension 3 months before only. Please clarify

[manci]

The sponsor can assign a new CoS to you at any time but you must apply for a new permission not later than 3 months after the CoS had been assigned.