Solution
A) Using Timing with NI myDAQ
The Digital I/O (DIO) lines of the NI myDAQ are software-timed, which means no hardware timing modes can be used with them. To avoid error -200077, don't use a DAQmx Timing VI in your digital tasks.
The default behavior of any created DAQmx task is On Demand samples: Every time the Read or Write function/VI executes, the device produces the requested samples as fast as possible. In this mode, the Sample Quantity attributes/properties are ignored. For more information about the sampling modes, refer to the NI DAQmx help document: Sample Timing Types.
B) Using a Trigger with NI myDAQ
There are Programmable Function Interface (PFI) lines on board the NI myDAQ, meaning that it can be configured as a general-purpose software-timed digital input or output, or it can act as a special function input or output for a digital counter. Nevertheless, these lines are not wired internally to be used as trigger sources. Therefore, it's not possible to configure a DAQmx Trigger VI in tasks that use NI myDAQ devices.