Processing time for H1-B Extension PP after USCIS Returned Check

My H1B extension petition with premium processing was received by USCIS on Mar 30th 2017. I got a response back from USCIS on April 19th stating that since the 15 day window has passed and they have not processed my application yet they are returning my check. However it stated in the notice that USCIS will still consider my application for a PREMIUM PROCESSING service . Any idea how long this process can take ? Will it be days or weeks or months ? If anybody can answer from past experience it would be much appreciated.

The notice date on my form I 797 C is April 17th 2017. The USCIS location is the Nebraska facility.

Got approval notice yesterday. Hope it helps folks sailing in the same boat.