TB doesn't alter the dates of the imported messages, the created dates should be the same. You're probably looking for the recived date. TB can't import those from OE, because OE stores other things than TB. OE claims that messages are received at the moment they end up in your mailbox (that's the time and date of the last Received: header), TB considers a message received at the moment the message gets sorted into your local message base. As OE doesn't store that tiome/date TB can't import it, so TB uses the import date as received date. There's no posiible fix, TB can't restore data that aren't kept.

However, when you sort the messages in order of creation date, you'll have them in the correct order. (Unless your contacts have their computer clock displaying faulty values.)