H1b Extension ; Receipt Time

[govindp]

Hi
My H1b extesnion was submitted on feb 10th at nebraska service center ( current h1b is valid till march 1 ).
Does anybody know how long it takes ( approx ) to get the receipt notice?
I want to convert to premium processing and for that i need the receipt number.

Thanks in advance !

 

[ginnu]

15-20 days after received by service center