This modem (and a few others, but I only tested the TM602A) have an algorithm to accept a different password every day.

This password generator gives you the ability to generate a list of passwords for a bunch of days at once.

The start and end dates are basically the first and last day for which you would like a password generated. Just enter the day, month and year for each of them and press the "Go" button.

If you want a password for a single day, you enter the same date for both. This is actually the default, i.e., what you get automatically when you open this page: today's date on both start and end dates.