The state Board of Correction has approved the eligibility of 257 inmates for early release under a new state law to ease prison overcrowding. For the third time this year, the board used the Expanded Emergency Powers Act, which is effective when more than 500 state prisoners are backed up in county jails. Prisons spokeswoman Dina Tyler says county jails were housing 680 state prisoners as of yesterday. The total state prison population was 13,406. Two weeks ago, the board invoked the Emergency Powers Act to let up to 630 parole-eligible inmates out of prison up to 90 days early.