Each place now has a timezone field and this is used to set the default timezone for any logs to or from that place (kind of obvious really...)

When you're adding a new place, you can choose the timezone or just click the "Auto-detect" button which will use the geonames.org web-service to determine the timezone.

I have been able to fill in most timezones for places that have been created to date.  Have a look at the Places configuration page though as you may have one or two that you'll need to set yourself.

If a log doesn't match any places it will default to the timezone you've set in your Profile page, and the timezone for a log can always be edited if you want it to be something different.

-- Tom