Do you mean if you claim it from the gift window once you're fully logged in? If so, then no it does not activate. You have to manually activate it from the character select screen. There will be an "Advance Character" button under your character's details (name, morality, power etc.) and when you click into that it will then give you the option to advance to CR 255. But beware - there is no confirmation window asking you if you're sure you want to use it. Once you press the Skip to CR 255 button it logs you in and advances your character, so be careful you don't accidentally do it. Once you have claimed it it will stay on your account until you're ready to use it. There is no expiration once you have it. And yes, the CR 10 mission and On Duty event are the only two places to get Spooky Bites outside of the Marketplace.