Need help. RFE deadline - does "received by" mean mailroom delivery or when they actually log it and provide the receipt date?

Stressing out here. My RFE response deadline is Feb 9 and package is still in transit due to weather delays in Texas. The package has arrived in Texas, however, severe road conditions have caused a three-day delay in delivery to the USCIS mailroom.

Quick question for anyone who's been through this - when USCIS says they need to ‘receive the response by the deadline (in my case Feb 9), does that mean:

1. Package delivered to the mailroom/lockbox (delivery confirmation date)

or

2. When they actually open it, scan and log it into the system (can be days?)

I've heard it's (1) but want to confirm here. If it’s not the case, what are my options since (2) can take several days. Note: this is a premium processing case.

Also - Feb 9 is a Sunday. Does that mean my actual deadline is Friday Feb 7? Or does it extend to Monday Feb 10 since they’re closed on the weekend?

Thanks in advance.