SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6e54a5e714b90114ea86c7859f09bb6931df7d20af936304ad151657af005b58' 
  AND token = 'g6uU+LjNupoyrUeDPpJrpuxdPYWelE1twXEw1fa6mH0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00051

JSON explain

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