SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '68fd21b2e57af901a5a4d4bd4903da1dcd5926632c3087e51c2a2a1373724985' 
  AND token = '6VJ9QVp2WSJOy++WCfPVTnYQM/keugXgU/YoLjUWzE0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00055

JSON explain

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