This should already be the case. You select the timezone's representative city, and the timezones are based on the zoneinfo database which applies DST.

For example, Europe/London isn't just UTC, it's a defined timezone with particular jump date rules.

Okay, so it just works without needing a setting being applied. Pretty sure I had to adjust my timezone on the ocportal site for DST changes, but maybe v10 is different. Thanks.

It's possible you had it set to UTC instead of London.

Oh wait, ocPortal site is kind of pre-v8, so really outdated, that may be why.

Yeah, was going from memory of the old site but on the current Composr site I am set to UTC+1. In the dropdown there is UTC (No daylight saving) which made me think nothing had changed with regard to the system determining when DST is in effect and automatically changing the timezone to match. Think it was on a vbulletin board where I saw the option in edit profile to have the system autodetect DST and update your timezone. Anyhow, if this is what happens with Composr, that's cool :) The vbulletin thing seems daft to have it as an option, it should be auto adjusting all accounts that it applies to, or none at all.