You will need a Form I-912 and need to supply all of the required doducments they indicate in those instructions. It should not take much if any longer to process with a fee wiaver if you submit the required fee waiver documents.
Lynne R. Feldman, Attorney at Law
Concentrating in Immigration and Nationality Law
2221 Camino Del Rio South, Suite 201
San Diego, CA 92108
phone: (619) 299-9600, facsimile: (619) 923-3277
Formerly Adjunct Professor -- Immigration law
University of Illinois College of Law
It will take longer only if your I-912 is rejected by USCIS because you would have to refile with the filing fee or additional documents to support a fee waiver.