SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '976286677ed09f8597f138005c463245b243b9f867f74ace1e2b6b05f1560a0c' 
  AND token = 'LJZYdmDOe0/TY+Kz6bJdS3cbBdqrOUEzlHvU/jCvFV4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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