How refresh token validity period works in WSO2 API Manager 1.10.0 and later versions.

If refresh token renewal not enabled(using

<RenewRefreshTokenForRefreshGrant>

parameter in identity.xml configuration file), we use existing refresh token else we issue a new refresh token. If issuing new refresh token, use default refresh token validity period(which is configured in

<RefreshTokenValidityPeriod>

parameter of identity.xml) otherwise use existing refresh token's validity period.
That is how refresh grant handler logic implemented in OAuth code

First i will generate access token using password grant as follows.

curl -k -d "grant_type=password&username=admin&password=admin" -H "Authorization: Basic X3kzVVRFSnNLdUNKZlBwOUpNUlNiV3drbFE4YTpmSzVPUzZFNEJfaW8xSFk1SGZsZjVPeWFreW9h" -H "Content-Type: application/x-www-form-urlencoded" https://localhost:8243/token
{"scope":"default","token_type":"Bearer","expires_in":3600,"refresh_token":"f0b7e3839143eec6439c10faf1a4c714","access_token":"03a3b01747b92ea714f171abc02791ba"}

Then refresh token with default configurations.

curl -k -d "grant_type=refresh_token&refresh_token=f0b7e3839143eec6439c10faf1a4c714&scope=PRODUCTION" -H "Authorization: Basic X3kzVVRFSnNLdUNKZlBwOUpNUlNiV3drbFE4YTpmSzVPUzZFNEJfaW8xSFk1SGZsZjVPeWFreW9h" -H "Content-Type: application/x-www-form-urlencoded" https://localhost:8243/token
{"scope":"default","token_type":"Bearer","expires_in":3600,"refresh_token":"4f1bebe8b284b3216efb228d523df452","access_token":"d8db6c3892a48adf1a81f320a4a46a66"}

As you can see refresh token update with token generation request.
Now i disable reneval refresh token by updating following parameters.

<RenewRefreshTokenForRefreshGrant>false</RenewRefreshTokenForRefreshGrant>

curl -k -d "grant_type=refresh_token&refresh_token=4f1bebe8b284b3216efb228d523df452&scope=PRODUCTION" -H "Authorization: Basic X3kzVVRFSnNLdUNKZlBwOUpNUlNiV3drbFE4YTpmSzVPUzZFNEJfaW8xSFk1SGZsZjVPeWFreW9h" -H "Content-Type: application/x-www-form-urlencoded" https://localhost:8243/token
{"scope":"default","token_type":"Bearer","expires_in":3600,"refresh_token":"4f1bebe8b284b3216efb228d523df452","access_token":"d7d2603c07fcadb9faf9593107bfbedd"}

In this case refresh token generated time will remains as it is. While having new access token and refresh token(but refresh token created time would be same).