It depends which service center you make application. CSC is the slowest center among the all and it usually takes over 3 months, whereas other centers could process EAD in less than a month. Additionally, is this the 1st EAD application or renewal?
After 90 days, you still can make infopass appointment in local office, but local office cannot issue any Interim EAD any more, but you still can obtain Interim EAD from Center Facility with the help of local office, namely local office will help you contact CIS for your Interim EAD from Center Facility other than local office.