Sorry, total noob Citi Double Cash questions here...

For context: I have a brand new Double Cash card and have begun using it. I also plan to apply for a Citi Premier card in the next month or two. Once I have the Premier card, I'd like to transfer the "cash rewards points" from my DC card to ThankYou points in the Premier account. My questions are around the timing (or expiration/other time-based limitations) of that transaction...

It looks like "Cash Back Rewards" appear under the "Double Cash Rewards" section of the website after the statement closes (first) and then after you have paid off your statement (the second "rewards", I'm assuming it works this way because of the card's name). Then there will be various options to redeem then (statement credit, check by mail, and convert to ThankYou points -- if you have a premium TYP-earning card, etc.). My specific questions...

• Is there any "expiration" date for "cash rewards"?
• Can they just sit there in my account and accumulate indefinitely and then be redeemed later?
• If I pile up a large amount of "cash rewards" now, if I wait months to get my Premier card, can I then convert those accumulated "cash rewards" to ThankYou points later?
• Are there any timing/expiration issues I need to be aware of?

Thanks for the help.