SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'ec151c99ad4c9a56f49160a73b24af50d85bd3fd42ba9ee0056f06440b98a265' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00013

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}