Given the long by default periods, and assuming the site works out, careers will have a huge number of uninterested CVs.
I don't know if this fits in your business plan, but I think a good way to avoid that problem while motivating the seekers to cooperate is to add a flag "Open for offers".
When the flag is selected, the CV is listed and the paid for time counts down. When the flag is not selected, the CV is no longer listed, but the paid for time doesn't count down. This should motivate people to go back and unmark "Open for offers" when they've found a job.