Enable debug logs and check token expire time in WSO2 API Manager

To do that you can enable debug logs for following class.
org.wso2.carbon.apimgt.impl.dao.ApiMgtDAO

Then it will print following log
log.debug("Checking Access token: " + accessToken + " for validity." + "((currentTime - timestampSkew) > (issuedTime + validityPeriod)) : " + "((" + currentTime + "-" + timestampSkew + ")" + " > (" + issuedTime + " + " + validityPeriod + "))");


Then whenever this call fails we need to check for this log during that time. Then we can get clear idea about validity period calculation.

To enable debug logs add below line to log4j.properties that reside in /repository/conf/
log4j.logger.org.wso2.carbon.apimgt.impl.dao.ApiMgtDAO=DEBUG

And restart the server. You need to do enable debug log in Identity Server side if you use IS as key manager scenario.

Then you can check how token validity period behave with each API call we make.