It should take 10 minutes with a transaction fee that isn't too low and with a few measures* instant 0-confirmation transaction can be relatively safe and used for transactions of, say, less than $1000 (given the resources required to double-spend if appropriate precautions were taken by the merchant, accepting 0-confirmation transaction for low-value goods can be safe).

*connections only to previously whitelisted and known honest nodes, no outgoing connections (UPnP off), etc.