I can't look at your VI, but try right clicking and selecting Properties>>Format & Precision and change to Absolute time. If you're using a chart, you will need to set the Offset and Multiplier properties in your code using a property node.
You can translate a string to a timestamp by converting each element to a number and building a time cluster. The attached VI shows an example of the technique, but it's not finished and probably has some bugs. If your format is set, you can write a small piece of code to do this.