for me it took 6 months to get petition approved

So did you get approval starting that date or retrospectively from oct 1?

it will take 9 months or more time. sometimes you will get RFE or administrative process. so better to do premium process.

@Kiran A is this for first time H1b or extension?

H1B transfer

are you applying from outside the US and need consular processing?

No its COS from F1 to H1.