Gorgona was flooded out during the creation of the Panama Canal:
http://cdnc.ucr.edu/cgi-bin/cdnc?a=...9130719.2.44I haven't found a map showing Gorgona at the time, but it was only a few miles from Cristobal. So it appears the letter was received the same morning it was posted from Cristobal, though I cannot make out the time it was postmarked in Cristobal.
Back to the question about commercial usage, I think all usage at the time, even on the first day of issue, would have been commercial. First day covers as philatelic creations come a bit later. US stamps of that era with postmarks on the first day of issue are quite scarce, and valuable. There would be no premium for "first commercial use" for a cover issued three days after issue, ordinarily. The 2014 Scott US Specialized values this stamp on cover at $55.00. And that takes into account that only 50k were issued, and it was replaced by Scott #23 on November 25. The latter has a Scott CV on cover of just $3.25.
It is a great cover, and if I collected Canal Zone (I've a few of the airmail stamps, but have never gotten into it further) I would consider it a great find. But figure the value at some fraction -- my guess would be 40 to 50 percent -- of Scott's $55.00.
A Canal Zone specialist might say otherwise, though.
This is my third edit now, but something else occurs to me. The Chinese characters and the stamp were probably placed there by the sender, not the receiver. Note the placement of the stamp. That would be an odd place to to place the stamp, unless the Chinese characters were applied first, forcing the stamp to be placed to the left of where it would ordinarily go. If it were my cover, I would certainly try to find someone who can read the Chinese characters. A wild guess is that they are a benediction or proverb or some well wishing of some kind. The red stamp probably is a mark of the individual who wrote the Chinese script. I lived in Taiwan in the early 1960's and remember such rubber stamps were quite common.
Basil