Online visa Application start Date and submission date

Hi
I am applying for switch visa application.My question is
I have create the application 25 Oct. and my start date is 21/02. My sponsor will issue COS may be after 22 Nov(within a 3 months of the start date).
Can we create(not submit) my online visa application 3 months before the start date ?

You can start the application form as early as you want and hope UKVI do not amend the application form before you submit. If they do, you need to start over again.