Bitcoin-Qt listing all Transactions as occurring at same date and time
I've also had the same issue whereby importing a private key using RPC Console importprivkey will rescan and tag it with the time which the rescan takes place in btc-qt. 

Even Multibit which uses the following format for private key (*.key) files is only dated such that the date corresponds to what is assumed to be the key's creation date:
Kwnononok7xQwSNIPSNIPSNIPSNIPssthcheckth1s 2013-09-18T09:42:28Z

As mentioned, the Blockchain is not being consulted for transaction history - a major flaw IMO.