Plot digital wave Vs text wave

You have two options:

1) Convert your date & time text into regular date/time data. See here:

For this you would need to convert your text wave with a small script, which is however not difficult. If your date/time information is equidistant, you could even use wave scaling and omit the x-wave altogether.

2) Use your date/time text data as tick labels. For this, create a plot just from the digital data, then open the Modify Axis dialog. Go to the Auto/Man Ticks tab and select User Ticks from Wave. There you can load your date/time data in. Note that this will create a tick for every point in your data, which might get too crowded in the graph. Read more here:

Thank you! I have tried both. As you said, second option shows too much ticks. For the first option, I plot the image shown below. How to remove the marked default year and date? 

Go to the Ticks and Grids tab inside the Modify Axis dialog and set Suppress Date for Date/Time Tick Labels.

You might even want to set the horizontal axis Time Format to Elapsed.