The closest that you can get meaningfully, is the timestamp of the block. The timestamp in the block is usually very close* to the actual time that block was found, and is absolutely sure to be within the fuzzy window that the network defines for validity.
* And by "very close", I mean within the "reasonable accuracy of a few minutes" that you are asking for.
Interesting... I've been looking at just that solution. But the problem is that the address-transaction function only gives you the block height, and unless I'm mistaken, blockchain.info doesn't have a function for getting the block from it's block height. My bitcoin-qt client doesn't give me all the blocks in the block chain, either. What's a poor coder to do?
bitcoind getblockhash 291050
bitcoind getblock 00000000000000004642ed8eb619f2f84aaf201dbf0ba5fc87c425d040455d5a