Displayed Time Format
The viewer shows the time of day in at least one place, that being the right end of the menu bar. There it shows time in either 12-hour or 24-hour format, and either PST (Pacific Standard Time) or PDT (Pacific Daylight Time). The menu bar time format can be selected in Preferences → User Interface → Top Bars → Time Format.
The viewer may also show timestamps in chat and the Conversation Log; those are also PST or PDT and are always 24-hour format. As of Release 5.0.7.52912, if you show timestamps for Teleport History, you have the choice (in Teleport History → Gear menu → Select Timezone) of UTC/GMT (7 or 8 hours before SLT, depending on Daylight Savings), SLT or your Local Timezone (all in 24-hour format). Group Notices display PST/PDT in the Group Notice Toast (in 12-hour format), PST/PDT (24-hour Format) in the Notifications Window and in the Group Profile Notices in GMT/UTC in 24-hour format.