Interesting question ;)
The calendar definitions doesn't know an attribute to "hold" that date.
But with Reminderfox you are in a better situation. We generate the unique identifier for each event (or todo) based on the actual date/time (with some more random numbers). So if you're able to access the Reminderfox ICS data file you will find for all events/todos generated with Reminderfox that UID. And you have to decode that "only".
Not that difficult, use the error console and enter the appropriated string, like this:
UID:1327532400000-940074372
new Date(1327532400000) = Thu Jan 26 2012 00:00:00 GMT+0100 (CET)
Isn't that easy?
Guenter