What exactly are timestamps? When do we see them in IOTA? And what is the correlation between timestamps and smart contracts?
The transactions of e.g. Ethereum have a fixed order becaue they are in a blockchain. Because IOTA stores it's transactions in the Tangle, we don't have a sequence. In order to execute smart contract consistency is required. To achieve something similar on IOTA, mandatory timestamps are necessary.
You can already send timestamps with your transactions but it's not enforced, just arbitrary. Timestamps will be mandatory soon™ (We don't know when exactly) and when they are smart contracts will be possible to some extent.
IOTA may never be capable of as complex smart contracts as in Ethereum, but we will definitely see something similar to it.