How do I change the time zone or use a 12-hour clock?

Right-click the time axis at the bottom of the chart: Time zone sets the zone the chart shows times in, and 12-hour clock switches the time labels.

Right-click the time axis, the row of dates and times along the bottom of the chart:

Time zone sets the zone the chart shows its times in.
12-hour clock switches the time labels between the 12-hour and the 24-hour format.

The same menu holds Session breaks, and Extended hours shading on markets with a regular session.