The leadership field in your node config file is not mandatory, by default it is set as follow:

leadership:
log_ttl: 1h
garbage_collection_interval: 15m

• log_ttl describes for how long the node will keep logs of leader events. This is link to the data you receives from the REST leadership logs end point;
• garbage_collection_interval describes the interval between 2 garbage collection runs: i.e. when the node removes item logs that have timed out