Hello lklaverstijn,
Having the task scheduled on top of the already existing startup item will not cause any issues, however, it will cause the Fences configuration window to load when called for the second time. Therefore, I would indeed recommend disabling the startup simply for the sake of testing that task.
Regarding the time delay set in the task, it is just a base value we found to be appropriate for the average computer and can certainly be adjusted if you feel it is too long or not long enough. To clarify however, the task is not delaying the startup process in any way, rather it is being triggered by logging onto your system and after 10 seconds have passed, your system will run the task. As a result, this should not result in any delays in your boot time.
If the task does not help, please create a ticket so we can look into this issue further. Please see the following article for information on placing a ticket:
https://esupport.stardock.com/index.php?/default_import/Knowledgebase/Article/View/377/24/how-do-i-get-official-support--how-does-support-work