Thank you for contacting Avenza Support! The date and time stamp are within the KML, however, that may not become visible in Google Earth. If you open the KML with a text editor, you should see a <TimeStamp> tag, and within the <when> tags beneath will be the time that the placemark was created. If you exported placemarks with photos, a KMZ will be exported. To access the KML, extract the KMZ in File Explorer, and then open then KML within the extracted Folder with a text editor.
Maintaining EXIF data on export to JPEG will be implemented in Avenza Maps 3.4, which will be available in the near future.
If you have more questions about this, feel free to contact email@example.com