When using /questions (e.g. like this)), dates are represented by a number. I'd like to know how I can convert a number to a date. For example if I have 1293840000, what date does it represent?
The number you're looking for is the Unix timestamp, the number of seconds since January 1st, 1970, 12am UTC. So 1293840000 represents Saturday, January 1, 2011 12:00:00 AM. This is documented in the API as well:
All dates in the API are in unix epoch time, which is the number of seconds since midnight UTC January 1st, 1970.
You can use an online converter like this one to manually convert from and to human readable dates, and your programming of choice certainly has functions for this as well.