It depends on what you want -- but, as far as I know, the "publication date" in CreateSpace is informational only. If you want it to have a specific date, I believe you can set that date regardless of when the print edition is actually available for sale (and it doesn't affect the availability of the print edition). If you don't care how that field reads, you can leave it blank and let them fill it. Others may correct me, but this is my understanding from my recent experience, and it's what I'm going forward with for my next print release this month.
The turn-around time from when you accept the proof to when the book is available for sale seems very fast to me. I believe mine was well under a day. If you specifically don't want the print edition available for purchase until the Kindle edition is ready, I recommend waiting on proof approval until shortly before the Kindle edition is released. (Don't forget that there is a delay between submitting your materials and when it's even possible to accept the proof.)
Using my next release and my own preferences as an example, the Kindle edition is set up for pre-orders with the 27th being the release date. I will set the date in CreateSpace to the 27th, but I plan to accept the digital (online) proof next week, basically as early as I can, so I can order copies and hopefully have them in hand in time for the launch party.
