Set processing order of added items

I have an external Applescript which does stuff with items added to a folder. The processing take several minutes per item.

How can I get Hazel to process the items in the order they were added to the folder?

In my testing the order seems random.

E.g., I added items (with a slight pause between each) in this order:
1, 2, 3, 4, 5
But Hazel processed them in this order:
1, 3, 4, 5, 2

You can't really rely on a specific order in general. You may be able to add conditions to the rule to do it though.

Add a condition like "Date added is the 1 least recent". That will match the file that was added first. The caveat here is that the rule must move the file somewhere else so that the next file will end up matching the rule.