It's 30 days to approve, but if by the end of the 30 days they decide that they cannot, they get a another 45 days to investigate it. This actually gives them 75 days to make up their mind.
After 75 days you think it would be over... But you would be wrong. The president then get's final say if he doesn't agree with the CFIUS. So he is allotted 10 days to make up his mind. In total they get 85 days.