The DNG converter does not actually "convert" your raw images, it rather creates a additional .DNG file of that image.
It uses the computer date as a source for the time of the creation of that file. However, the original date and time will still be part of the metadata for each file.
Also you may post this thread to Digital Negative (DNG)
You are not reading me. I am aware that it is a new file and will have new date attributes. But the metadata is changed as well. The metadata has the date that I did the convert.