There is no software update for the OnTime Pro application. I've checked the official website and there is no mention about updates and their availability which means that the product is either discontinued or available only in its current form without a possibility to download it anymore.
The only thing that is now viable is the the contact option that will get you in touch with the developers.
Use the following email to get in touch with them:
firstname.lastname@example.org. This way you can ask for details related to updates and the current status of development.