***I see this is an old question, but doesn't have a fully working answer yet.***
The logic behind finding whether a new item is there or not is to filter your list to the "new or not" value and count the matches. If the count is 0, it's a new value, if it isn't, it is an already existing one.
So in general it looks a bit like this:
If(CountRows(LookUp(YourList, ColumnName=EntryToBeExamined)) > 0, true, false)
Your question being "Is it an existing value?" or "Do I need to update LOETime?". Then write your next action in the true branch, and if there is nothing to do with the false, you can skip it.
In your case,
YourList is the SharePoint list you use,
ColumnName is "Mix",
EntryToBeExamined is either from a variable, or the source of input field on your form, textbox, dropdown, etc. But it's very important to be an exact match, otherwise you'll have to complicate with putting both phrases you are matching all Lowercase or Uppercase for example.
This determines, whether the value is new or not. With the above case, your true value is, when the value already exists, and you want to update the LOETime to 0.5 seconds.
If it makes more sense to you, to turn the true/false result around, you can always check, whether the count equals to zero, that way, you're checking whether there isn't any matching results. So in this case you basically ask the question: "Is this a new value?".
In this case, you'd have to do the LOETime setting in the false branch...
