Write to File, Write LabVIEW Measurement File, Write Spreadsheet File, Export Waveforms to Spreadsheet File, all can be used. How often you write is not up to any of these but how often you call them. You have to add some code if you only want to write periodically. One way is to use the Elapsed Time function. You can wire the Boolean output to a case statement or wire it to the enable input of the Write LabVIEW Measurement File Express VI.