code: def epoch_to_dttm(cls) -> str:
      return "(timestamp 'epoch' + {col} * interval '1 second')"
  
imports: from superset.constants import TimeGrain
  from superset.db_engine_specs.postgres import PostgresBaseEngineSpec
label_desc: Use image node_id 1 for calling the NetezzaEngineSpec obj's underlying member method code with example usage: obj.epoch_to_dttm(cls) and returns: str