Is it possible to create a 1 of 2 multi-sig address in which only one of the keys is time-locked and the other can sign any time?
only one of the keys is time-locked
Keys aren't time-locked. Transactions are. However, Bitcoin now has an opcode for this purpose: OP_CHECKLOCKTIMEVERIFY.
Essentially, it forces the transaction to have a lock time further in the future than its argument, otherwise the transaction is invalid.
In your case, the script would look like this:
OP_IF <this pubkey can spend at any time> OP_CHECKSIG OP_ELSE <block number> OP_CHECKLOCKTIMEVERIFY OP_DROP <this pubkey must wait until block number> OP_CHECKSIG OP_ENDIF
The spend-anytime key can redeem the transaction with
<Sig> 1 <above script>
The other key can redeem with
<Sig> 0 <above script>
but only after the given block number.