Hello,
In the plugin configuration (via the Joomla plugin manager), you can configure in which "position" you want to display the countdown.
Thanks to that setting you can change the "slot" in the product page without having to perform a view override.
Now regarding the product listing ; that plugin was originally designed to display the counter in the product page only ; it would require some several modifications in the plugin source code to handle a product listing since the given data is not exactly the same and the view is using an unique ID (so it's not possible to have several countdowns in the same page).
These are not impossible tasks but would require some adjustments.
Regarding the display of the countdown depending the sale end and not the discount end is a really good idea of improvement.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.