Like everything in this process processing times vary from city to city and case to case.
In theory the EAD **should** be issued within 90 days of the date that your NOA is sent out. I think that the interim EAD proramme (where a temporary EAD is issued by your local office if the regular one is not issued within 90 days) has been scrapped by the INS. I'm sure there will be some other threads around about this.
In any case, plan for it take the full 90 days and hope you get lucky. Mine took nearly 5 months and I was denied a temp EAD even when the interim EAD program was still operating.
Hopefully you'll be lucky and you EAD will be processed quickly.
Best of luck
Mark