That is correct: If you delete a file and recreate it within the polling interval, adTempus will not know that it is a new file.

The File Trigger works by polling (scanning) the folders at the polling interval and comparing the state of the folder to the previous state. By default this happens every 60 seconds. It's not an instant event-based thing. It's only looking at the file name; it can't tell that a new file is different from an old file that had the same name. So it needs one cycle when the file isn't there so that when it appears in a later cycle it knows it's new.

Depending on your scenario you might be able to use the option to trigger when the file is modified. This works by looking for two files with the same name and comparing the timestamp. So if you delete the file and recreate it within the interval, it will be seen as a change.