SIC hours acquired while
performing the duties of PIC under the supervision of a
qualified PIC may be credited toward this requirement.


This does not mean SIC 121 time. you are not performing the duties of a PIC. are you responsible for the aircraft and its crew? are you signing the release and asuring that all things are in order for the flight? NO. you are just performing the duties of the flying pilot. the 250 hrs is a solid number. credit is giving for SPIC (Supervised Pilot in Command) flight time according to the FAA, but remember some airlines have their own requirments for captains in addition to the FAA mins. you are not SPIC when you fly 121. you are are SIC. the time counts towards your TOTAL TIME REQUIRED (1500) but not towards the 250 hrs PIC REQUIRED.