Working for old emplyer while waiting for decision of tier 2 sponsor switch

[Fcjl22]

I have just got an offer for a new job but my visa is expring next month. My questions are

1. Can I apply to extend my T2 for the new employer now but keeps working for my current employer? I know that due to the corona, you can start working for the new employer as soon as you submitted your application.

2. Is it 3 months/90 days the earliest you can apply before the starting date? Since my current visa exprires 15 July but the job starts 1 October, am I ok to apply to extend my T2 after 1 July but before 15 July? Will I be counted as overstay since the job doesn't start untial 1 Octerber?

Thank you.