The purpose of Form I-907 is to request USCIS premium processing for certain applications, such as I-765, I-129, I-140, and I-539.

This page shows the current USCIS processing time for Form I-539 which is used for an extension of status or stay. This data is frequently..

This page shows the current processing times for Form I-539 if you have applied for a change of status to H4, B1/B2, L2, F, M, or J visa...

Change of status from H1B to J2 visa is a very rare case, usually, it's the opposite, people on J visas try to get H1B.

This I-485 processing time for employment-based adjustment of status is based on how long it took USCIS to complete 80% of adjudicated cases