SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '794f896215f7af27491854395bc161cda58922af2d407d9d5b086e3a9f840c39' 
  AND token = 'YSXEKwKMaWnCDrs9sugexrZJ/u3AiVUzEqMWLZW+AvI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}