Timechain describes Bitcoin's chain of blocks with an emphasis on demonstrable ordering. Each later header contains its predecessor's hash; it is neither a separate protocol nor a new unit of time.
A block points to a particular predecessor, not merely its height. Changing an older transaction changes its Merkle Root and block hash, breaking the next link; rewriting history requires new work. [Bitcoin whitepaper] [Bitcoin Core validation source]
Two transactions can spend one UTXO to different recipients and reach nodes in different orders. A valid history cannot contain both, yet block inclusion does not prove which transaction was created or broadcast first. [Bitcoin whitepaper] [Bitcoin Core validation source]
A node selects the valid branch with greatest accumulated work. Block count alone fails when difficulties differ; chainwork represents expected work, not a measured number of miners' attempts. [Bitcoin whitepaper] [Bitcoin Core validation source]
A new mainnet block must be later than the median of the previous 11 block times and no more than two hours ahead of a node's clock. Its time can therefore be lower than that of its immediate predecessor. [Bitcoin whitepaper] [Bitcoin Core validation source]
Ten minutes is a target average, not a timetable, so height does not determine an exact date. BIP 113 uses median time past for absolute nLockTime; satisfying it permits inclusion but does not fix when inclusion occurs. [Bitcoin whitepaper] [Bitcoin Core validation source]
Two valid blocks can compete at one height. The branch with more work can disconnect the other; its transactions may reconfirm, become unconfirmed, or conflict. More confirmations raise rewriting cost, not absolute certainty. [Bitcoin whitepaper] [Bitcoin Core validation source]
getblock at verbosity 1 provides height, previousblockhash, time, mediantime and chainwork. The hash link gives position, time is a header claim and mediantime is a median; none alone proves the exact broadcast moment. [Bitcoin whitepaper] [Bitcoin Core validation source]
For the clearest picture, read this entry together with Genesis Block, Proof of Work, Transaction, Full Node, Difficulty adjustment. The reverse links also lead from Bitcoin Whitepaper, Genesis Block, Proof of Work, Full Node.