#access_token

original source : http://stackoverflow.com/questions/13851157/oauth2-and-google-api-access-token-expiration-time

You shouldn't design your application based on specific lifetimes of access tokens. Just assume they are (very) short lived.

However, after a successful completion of the OAuth2 installed application flow, you will get back a refresh token. This refresh token never expires, and you can use it to exchange it for an access token as needed. Save the refresh tokens, and use them to get access tokens on-demand (which should then immediately be used to get access to user data).

EDIT: My comments above notwithstanding, there are two easy ways to get the access token expiration time:

It is a parameter in the response (expires_in)when you exchange your refresh token (using /o/oauth2/token endpoint). More details.

There is also an API that returns the remaining lifetime of the access_token:

https://www.googleapis.com/oauth2/v1/tokeninfo?access_token={accessToken}

Now, the default time for access token is 2 hours. It's not enough for us to do some task that need a long long time. (Ref: http://developers.facebook.com/blog/post/2011/05/13/how-to--handle-expired-access-tokens/)

Since the offline_access is predicated, FB have another end point that help us renew the access token. We can renew it for 60 days and you can do this many time.