I contacted Customer Service (CS). Indeed, it is at the time of order, or a provable agreement in writing. I ordered Oct 2nd, and was able to add referral code for $100 free super charging, and referral link as a non-performance Model 3 on Oct 5th, which is the day it was announced.
Fortunately, I had an an EMAIL with the Owner Advisor (OA) stating he linked the referral to my order on Oct 5th to help backup my claim.
I pursued the 6-months free supercharging (foggy on the sequence of events) when I initially contacted Customer Service today. I ended coming up short as I didn't have any records saying that I was planning to cancel my order and place a new order to take advantage of the 6-months free supercharging. While on hold, I was able to trace back that indeed the OA associated the previous offer from Oct 5th ($100 SC credit + non-P referral). I did recall a phone call to CS asking about the pro/cons of cancelling and reordering for the referral credit and reservation credit to properly show up in my online account, and was told to not cancel.
To my dismay, I find out that the Referral Department is working this currently, and only because I sent them an email today. I am shocked that the Referral Department wasn't already working this from being assured by the Owner Advisor and Delivery Advisor. There is possibly confusion with the Oct 5th $100 credit + referral link, and the subsequent (as of today) 6-mos free + referral link for all Model 3. It will be more waiting.
For me, not much advantage of the 6-months free supercharging vs. $100 credit. I charge at home, and not many road trips planned, so perks are about the same. I am more bent over the referral link because I am referring myself, and had a sibling order a Model 3 as well. I can't justify buying a Wall Connector, so hoping to get it for free as a referral gift/perk.