A community user pointed out:

if I config the setting of timezone,the time in the graph bar of bottom is not changed.

Indeed this is true. As of Brim commit 76f506a talking to zqd commit 42103ef, here's what the UI looks like after importing a test wrccdc pcap:

If I change the Timezone Preference from its UTC default to US/Pacific, we can see the values in the ts column change, but the X-axis does not.