Yes, you are correct! Your FCT will expire in 31 days after activation.
If you purchase a FCT and not yet activate it, it will NOT expire! You will need to activate it manually and it will expire 'example: in 31 days'.
The FCT is used to download routes, trains, scenery, locomotives, rolling stock and more from the DLS 'Download Station' at a better speed! Without a FCT, downloads could take more than a day to complete depending on the file size.
To access the DLS, launch Trainz! Content Manager, then change the 'installed' filter to 'Download Station'. Here you can also change filters to find specific content..
If you have an internet browser that supports FTP links. You can visit the Download Station via this link
https://www.auran.com/
If however, for some reason that you can't somehow download a certain route, locomotive or rolling stock or can't seem to find a certain dependency for the route, locomotive or rolling stock visit
https://trainzland.ru/ you will need to be a member to download. Remember, not everything is here! So, if you have missing dependencies generally this means you are missing a payware route. If there are still missing dependencies, these are 3rd party assets which were never made available on the DLS and most of the sites hosting the asset is gone! So, if you run into that. Grin and bare with the dependency being missing
Hopefully, this answers your questions