Incidentally, why are you plotting Date and Time on the X Axis? Do you really need to know the date that each data point was recorded? Wouldn't "Elapsed time" (in seconds, minutes, or hours, as appropriate for your data rate) be more useful? If so, you can easily convert "Time" to "Elapsed Time" by creating TimeStamps (as you've done) and subtracting the initial TimeStamp (Time-zero) from all of them. The difference of two TimeStamps is a Dbl, and represents the number of seconds between the two TimeStamps.
Thanks for the suggestion, but my requirement is that i need time stamp in hour and minutes (seconds may be there), and i also need date.
But date should be in title label of XY chart, if my logs is for single day then that date will be written on title label.
If the logs are for multiples days, then i will take the date from the first line and and then from the last line, and the display the title as from this date to this date.
I think this can be done using property node of xy chart, create -> property node -> label -> text
Instead of saving csv data to a text file and then reading it and plot the XY graph, is there is a option to plot the csv data coming from the serial port dynamically into XY plot with timestamp on X axis and temperature on Y axis.