When printing data on SMARTDAC+ standard universal viewer, can I change the length of time per grid mark on the time axis?

Yes. Under File > Print settings, set Waveform print settings to Multiple pages, then you can change the grid (waveform printing grid) spacing along the time axis.
When Waveform print settings are set to "1 page," the waveform printing grid is automatically adjusted and cannot be specified by the user.