>> the deadline for seeds to *arrive* to the host is Thursday, January 21.
Ahh, now I see this:
>> Trading End, Send Seeds to Host: January 11, 2016 (8 days)
So trading ends Jan 11 and the seeds must arrive at your house by January 21.
That's ten days for packing and transit.
I'm back to "indifferent", meaning more time might be nice, but is not needed. I assume that even priority mail can easily take 4 days, and that leaves up to 6 days to pack and mail it.