I flew my 4 flights on Nov 5, and had to ask to claim two flights which were missing from that 4-segment run. They posted the flights immediately, and I was re-qualified immediately for 2018. Got my new card in the mail today (Canada), good till Nov 24, 2018.
For another poster, two years ago, I flew my four flights on the last day of the valid card. I was dropped to silver, until they posted, and then was flipped right back to Gold, automatically. I didn't know if it would work or not, leaving it to the very last day, but I had to plan my flights while I'm in Europe, so that was the only time I had to do it. Was very glad it worked.