The MathJax developer's drop-in hour is at 16:00 UTC (noon Eastern, 5PM UK time) on July 23rd. You can join via the following link:
Note that you must use the Chrome browser (and actual Chrome, not another chromium-based browser) in order to use the Sococo site (sorry about that). If you have trouble using the link, post a reply here, and we'll help you to get in. Note that the link will not be valid until 12:00 eastern time, and will give a message to that effect if you follow it before then.