the achievements and user card, etc.

what time do they get updated?

They will be updated in 24 hours.

no, like what GMT time, etc. Is there an exact time when they are updated

Nope. There is not exact time. They just update under 24 hours after you make your changes.

There is an exact time.
Forum updates at 8:30am 0 GMT, give or take some minutes

Sorry, i didn't knew about that.

To find that time in your country, just add up the hours in 8:30. For example, my GMT is +5, adding five hours in 8:30, the time in my country will be 1:30 PM.

To make the time conversion easier, use this.
http://wwp.greenwichmeantime.com/gmt-converter/

if they are updated every 24 hours my rank on fourms has stayed the same for weeks