According to the following description in the document,

The timer start event is a start event with a timing mechanism. A process can contain multiple timer start events, which are triggered at the start of the process, after which the timing mechanism is applied.

the customer thought that multiple start timer node can be defined in one process and these are executed respectively per defined timer.
However, if there are multiple start timer nodes, the process gets started by only one specific timer node.
i.e. in attached sample bpmn, the process always gets started by start timer node named 'cron-5s' and start time node named 'cron-7s' is never executed.

Here is engineering opinion on this behavior.

From the spec point of view you can only trigger one of them because multiple start timer events are the same start event (that would be the short answer)

so you will only will see one of the timers triggered at a time per process instance.

From the spec point of view you can only trigger one of them because multiple start timer events are the same start event (that would be the short answer)

so you will only will see one of the timers triggered at a time per process instance.

I would not consider this as a bug.

This is request to improve the above description in the document more accurately in order to avoid misread it like the customer.