Can I file for H4 EAD as soon as I receive the H1 & H4 approval ?

I’m on L1A and my wife is working using L2 EAD. My H1B (COS) is picked up this year. Can I file for H4 EAD as soon as my H1 and H4 approval comes or do I have to wait till 1st October to file for H4 EAD ? My I140 is already approved.

I think it can be applied soon after H-4 COS arrives. You still need to give a start date of Oct 1 or later, as H-4 cannot become active prior to that.