Lifetime, unless some rules will change and they are the same from long time ago (I suppose a year or more, based on my memory and usage of freebtc).
Atm if you have a balance $50 or more you will be able to unlock all reward bonuses (I call them "boosters" just to not confuse them with the bonus that increase evry time you play lottery and hi-low) and use them to get more satoshis from free rolls, also to get more points and lottery tickets if you are intrested in lottery, just remember that you can redeem one of a kind and no 2/3 or more. Ex: 1point booster + 1btc booster + 1lottery booster, NOT 2point boosters at the same time.
If your balance is $100 or more you also have NO CAPTCHA and this is one of the best thing, I really hate re-captcha and solvemedia is available only on pc not on mobile device (or at least that is what it is in my country...). Re-captcha can be really a pita   and I really hate this kind of captcha, i prefer solvemedia BUT I use mobile to claim on freebtc so I'm happy to not have any captcha and it take less time to claim (15sec?) so I can claim even if I'am working. Ok, that was my opiniono based on my needs...