My dear fire breathing friend,
I think you will find the E series user manual section of counters useful.
Here is the short version: The 6023e does not support hardware timed digital out. Fortunately for you, you are not doing a digital output task. You have selected a counter output task. The counter is outputing exactly what you have told it to output; be high for 10m, be low for 10m. So long as the provided clock source is not slower than the output you are asking for, the task should provide the same signal regardless of the frequency of the input clock.
No error has been thrown because the card is capable of this kind of output.