Story Teller achievement - Calendar Man

In order to get this achievement, you have to visit the Calendar Man in his cell at special dates.
Starting New Years Day, he will more or less tell you which is the next date you should to visit him.

You can complete this by adjusting your computer's clock.
Start by setting your year to 2012. This is because some holidays change dates from year to year, to correspond with a certain day of the week or similar.

His cell is in the basement of the Solomon Wayne Courthouse. You can enter through the backdoor.

Enter the courthouse, and go down talk to the Calendar Man.
After he finished telling his story, go back outside, alt-tab to change the date, alt-tab back, enter the courthouse and talk to him again. Rinse and repeat.
I don't know if going out and in is necessary, but I wanted to give the game an opportunity to save the interaction and to load the area with the new date set.

The dates does not appear on the calendar besides his cell prior to the date being "completed", at least during my playthrough. But as mentioned, he will tell you when next to come see him.

The dates, in order, are as follows:

1st January - New Years Day
14th February - St. Valentine's Day
17th March - St. Patrick's Day
1st April - April Fools Day
13th May - Mother's Day 2012 (moving)
17th June - Father's Day 2012 (moving)
4th July - US Independence Day
16th August - St. Roch's Day
3rd September - Labour Day 2012 (moving)
31st October - Halloween
22nd November - US Thanksgiving 2012 (moving)
25th December - Christmas Day

After the final date/getting the achievement, Batman can go back to check on the Calendar Man, only to find he's escaped custody, leaving another guy hanging there.

Inspired by a few other guides found online, which I pilfered dates from to try completing this achievement. Notably, (this, by Moritz_M05, which got me started, and a few others. The (minor) issue was that other guides were not always clear on the process or that some dates would only be accurate for a specific year. So cred to anyone that made a guide for this prior to mine ;)