Google API expiration date is 1 hour, the problem is that I'm using the API in order allow users to use admin SDK features (List groups, add members to a group etc.)
No one can do any of that in one hour, that would require users to login to their accounts multiple times per day to manage their groups. A 1 hour expiration date is good if you just want to use Google to authenticate users.
How to increase that or is there any work around? Am I missing something?
Due to security reasons, you cannot change the duration of the access token's expiry. However, you can refresh an access token without prompting the user for permission if you requested offline access to the scopes associated with the token.