The server clock is set to UTC. Most of the forum users are in the USA. I have the forum configured to show "Yesterday" and "Today" for new posts. With the "Overall time offset" at 0, the same as UTC time, it shows around half as many "Most Online Today" (user count) and half as many new posts (split between "Yesterday" and "Today"), as it should to properly indicate the level of forum activity each day. To fix this, I put the "Overall time offset" to -7, to match the USA West coast.
The problem is, "Time Offset" in individual profile "Look and Layout" settings for all users is now incorrect by exactly +7. Is there a way to mass-update user time offsets so they don't need to figure out how to fix it on their own?