The amount of time is irrelevant, it is the amount of blocks you know have made it onto the block chain that gives you confidence. Six confirmations is six confirmations, weather it took an hour or fifteen minutes. After six confirmations there is very little risk that your transaction is going to end up on an orphan block, and as long as difficulty is in balance you are not going to have blocks solved every few seconds.
To revert a part of the block chain, you need to do as much work (in terms of hashing power) as was done to create the part of the block chain you're trying to revert. It does not matter whether this corresponds to one or to one million blocks. The frequency of blocks has nothing to do with security - it is only a trade-off between convenience and frequency of stale blocks (caused by network latency).
However, if you do not care about the security the block chain offers you (for example when you trust the sender not to try a double-spending attack), faster blocks are more useful.