More detailed description about "Duration"

[STRRL]

Each type of Chaos contains an optional field "duration". It introduces how long time a chaos experiment would affect.

A notable detail is the "duration" is calculated from the chaos experiment "created", not "applied".

The reason is Chaos Mesh prefers to use a determinable logic, because "applying chaos" requires time, and it might be failed at first, and succeed in the next several retries, backoff also need time. So the time "when applied chaos" is not determinable.

That should be updated.