For most of us, visualising date and time comes very naturally. I'm sure if we surveyed how people visualise date and time there would be some similarity among a plethora of different answers. However, one form stands alone for its ubiquity: a year-planner-style calendar. Twelve grids of numbers, each seven columns wide, four to six rows deep. Click on a number to do something with that date. Calendars are so simple for me and - statistically - you that it's easy to forget that a server-generated calendar like this is actually not accessible at all. The issue here is linearisation: flattening out the days of the calendar to a script that can be read - aloud, in braille... or by a search engine. A calendar in this form linearises to a script that reads like this:

January. One. Two. Three. Four. Five. Six. Seven. Eight. Nine. Ten. Yawn. Zzz. Snore... February. One. Two...
And so on. It's not useful to read out 365 numbers (366 next year) and expect users to just wait to respond when the day of the year they are looking for comes up. What is the accessible version? Well, the approach to take is to work out the linearisation we would like first. For example,
The following periods are currently available: the fifteenth of October to the twenty-ninth of November, then the eleventh of December to the seventeenth. Which date are you interested in?
Now, for a web page we might not expect to follow this pattern exactly, but the model is clear: list the calendar information, then query for a date. It looks something like this:

Periods Available

This is not bad even in a graphical user agent; describing calendars as schedules is not hard to visualise. Note that it would be perfectly possible to use Javascript to convert this calendar to a visual representation. Whether using Javascript in this way is accessible is open to debate. There is no reason screen readers can't execute Javascript. Some, I believe, already do. But there is a trend for graphical browsers to provide Javascript and for non-graphical browsers not to. I'd suggest if you are willing to forgo an approach that caters ideally to non-visual users, it's possible to do better. We can cheat the system, almost, by using alt attributes in images and image maps to provide the schedule version as above, but for the images and maps to supply the visual layout. In my latest project, I'm also using line boxes full of images rather than a table. This allows a single <a> tag to span a whole month worth of dates. But what it saves on the semantics, it loses on file size. A cheaper approach might be client-side image maps, especially of the lesser-known form involving <a shape=""> tags rather than <area shape=""> elements, or similar features in SVG. However, even with the approaches I've explored above, this is one area where I suspect there may not be a very solution that does equally well for visual and non-visual users. 365 dates worth of information is difficult to represent in a concise form. That's why we use calendars.