wallet passphrase
2. timeout       (numeric, required) The time to keep the decryption key in seconds; capped at 100000000 (~3 years).

Result:
null    (json null)

Examples:

Unlock the wallet for 60 seconds
> bitcoin-cli walletpassphrase "my pass phrase" 60

Lock the wallet again (before 60 seconds)
> bitcoin-cli walletlock 

As a JSON-RPC call
> curl --user myusername --data-binary '{"jsonrpc": "2.0", "id": "curltest", "method": "walletpassphrase", "params": ["my pass phrase", 60]}' -H 'content-type: app