As that board of your only supports static digital operations, that will be entirely system dependent. By static I mean that the digital state will be updated by a function call in Software.
As windows manages all the tasks in the computer, it's impossible to predict how fast the update will be executed and how big the jitter will be. But there will be jitter. You will be better of using one of the digital boards we have if you need to have a precise TTL waveform generation. I advise you the PCI-6534 baord. You can take a look at that board at www.ni.com.
Hope this helps.
Filipe
