If I use a multi-sig wallet for Bitcoin, and require a total of 2/3 keys to sign a transaction, does that mean that the total time would be limited to the time to confirm 2 signatures ie ~ 20 minutes if done simultaneously?

No, not at all. That is not what a confirmation means or how Bitcoin works at all.

A confirmation means that a transaction has been included in a valid block. It has nothing to do with the number of signatures. A multisig transaction just means that the transaction requires more signatures in order to be valid. The signatures are contained within the transaction itself.

The time to confirm a multisig transaction is the same as the time it takes to confirm a non-multisig transaction assuming everything else is the same (i.e. same fee rate).

And would it cost the same as a regular Bitcoin transaction?

It costs more because the transaction contains more data. Thus the absolute fee will be higher, although the fee rate will still be the same.