I-797B correction time period???

[italianjob]

Hi to all Adviser,
what is the correction time Preiod of I-797B , mistake in Sure Name : Kimar (instead of Kumar) , how many days USCIS takes for changing this silly mistake, I have original I-797B with mistake, they issued me Another one with correction then whats the time limitfor that getting new one with correct surename?..
thanks in advance..