Hi there, @ebonakdarian ...
I think I'm better understanding what you are saying, but let me check to make sure. Are you saying that when you go to edit a single assignment in your course, the "Due" date field includes both a place to enter a date and a time....such as this?

Is this where you are saying that you have to enter in the time for each assignment (of which it sounds you have many)? When I go to the other screen (explained in the Guide I had linked earlier) which allows me to edit due dates in bulk, it doesn't give an option to add in a time. Rather, I choose a date, and the default time of 11:59 PM is added to it...as shown here:

However, on this screen, I can manually change the time of 11:59 PM by just typing in the time that I want...for example, 2:35 PM. Canvas will accept this time once I save the page.
I then tried to copy the text from one due date field to another on the page. The strange thing was that even though I had a due date time of 2:35 PM, it switched it back to 11:59 PM on that same day. Weird! However, if I re-pasted the text over the top of the text that was in the due date field, the time of 2:35 PM "stuck" after I clicked away from that field. That does seem a bit buggy to me, to be honest...and probably worth of a ticket to the Canvas Help Desk team.
Now...the other option that you could use is a "Canvancement" (Canvas Enhancement) created by @James Jones. It works much like using this bulk due date page, but he does it via a script and using a Google Spreadsheet. Adjust All Assignment Dates on One Page - Instructure Community (canvaslms.com)
I hope I have covered much of what you have tried...so please let me know if any of this is helpful to you...thanks!
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