In Neo4j you can do it with something like:
MATCH (keanu:Person ) WHERE keanu.name = "Keanu Reeves" SET keanu.lastSeen = timestamp() RETURN keanu
or if you want to create the node if it does not exists you can do:
MERGE (keanu:Person { name:'Keanu Reeves' }) ON CREATE SET keanu.created = timestamp() ON MATCH SET keanu.lastSeen = timestamp() RETURN keanu