## timestamp
 
 set(now: `Compact<u64>`)
- **interface**: `timestamp.set`
- **summary**:    Set the current time. 

   This call should be invoked exactly once per block. It will panic at the finalization  phase, if this call hasn't been invoked by that time. 

   The timestamp should be greater than the previous one by the amount specified by  [`Config::MinimumPeriod`]. 

   The dispatch origin for this call must be _None_. 

   This dispatch class is _Mandatory_ to ensure it gets executed in the block. Be aware  that changing the complexity of this call could result exhausting the resources in a  block to execute any other calls. 

- Complexity 

  - `O(1)` (Note that implementations of `OnTimestampSet` must also be `O(1)`)

  - 1 storage read and 1 storage mutation (codec `O(1)` because of `DidUpdate::take` in `on_finalize`) 

  - 1 event handler `on_timestamp_set`. Must be `O(1)`.