Hello,
If you want to do contiuous acquisition then I would suggest following the link below:
Continuously Acquire Analog Data Using Buffers and Charting the Results
After you do continuous acquisition, you can multiply the sampling rate with the time that you want to specify and that will be the number of points of data that you want to acquire and then you can save that data in a file.
But if you want to do single point data acquisition using the simple data logger VI and software timed then you will have to introduce a case structure in the code such that you can input a time and then check for that user i
nput time and ask the VI to stop acquiring data.
Let me know if you have further questions.
Good luck and have a great day!
Regards,
Koninika
Applications Engineer
National Instruments
http://www.ni.com/support