"Autodetect" isn't a setting, it's a function that changes a setting. When you click "Autodetect" your browser runs a JavaScript which reads your computer's time zone setting at that instant and stores the value on the BG server. That stored value will not change until you run the JavaScript again.
TL;DNR: You still have to click on the "Autodetect" link each time your local time changes.
aahh that makes sense some of the sights I frequent are rather lacking in meaningful time settings and I had got used to this one being reasonably accurate as my pc tends to timetravel a little (it's old and cranky and needs regular persuasion, bit like a worn steam engine really,or me in the morning) M