If you have access to the private key of a BTC address or the recovery seed of a BTC wallet that held BTC at time of the BCH fork, you can split your coins whenever you want. Your BCH won't "expire" in any way and they will remain associated with your BTC / BCH address until you decide to move your BCH to a new address -- even if you have meanwhile transferred your BTC to somewhere else.
Caveat: If you manually split your BCH from your BTC it is recommended to move your BTC to a new wallet first, to avoid a potential compromise of your BTC stash.
Skza62,
Thanks for your post. When the Bitcoin Cash fork happened my bitcoins were stored in cold storage with Armory wallet software. I have still not done anything relating to claiming my BCH coins using my BTC coins because my Armory software has not been updated for 3 years. All I do is just keep my blockchain up to date using Bitcoin Core client software. I don't open my Armory software because as I mentioned it has not been updated for 3 years. You mention we have both BTC and BCH for those owning Bitcoin before the fork. Does this mean 5 years from now if Bitcoin Cash is at $50,000 and Bitcoin is at $1,000 I could legally claim a $50,000 Bitcoin Cash with my single Bitcoin. Or would I only be entitled to a fraction of a Bitcoin Cash coin valued at $1,000? I got my Bitcoins around 2013 and was advised to store them in Armory. I did just that, and have not done anything with them because I don't have the time to keep up with the Armory updates. But now I'm going to make the time to update my Armory.
HeRetiK,
I have private keys engraved into a piece of steel which is not as delicate as a piece of paper. You say my BCH will not expire. What I would really like to know relates to the future value of one coin over the other. If five years from now the value of Bitcoin tanks to $1,000 and Bitcoin Cash is at $50,000 does it really mean I lost $49,000 because Bitcoin devaluation?
I hope someone out there can clarify this devalation concern I have of one coin over the other and whether I need to move my Bitcoins around to combat future devaluation. Any comments will be greatly appreciated. Thanks in advance.