Server side date functions

Hi everyone,
Can someone please explain to me how to do date algebra on the server side?

There are 3 functions on the server side: Format Date, Date Add, and Date Diff, as shown in the pic below:

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All my attempts to use any of these 3 functions have failed rather miserably. I don’t know if this is me or it is a bug. I hope it’s me and that someone sets me on the right path, but it does look like a bug.

How to reproduce:

Let’s say that I have 2 dates, that I already passed to the server action (and I know it received it well, because I stored them in a table and are correct):
$_POST.ItemStarts
$_POST.ItemEnds

Date Add

Let’s say that I want to add 2 days to one of them. I use the Date Add function, which creates the following binding (I hope I’m using the correct term here) :

{{$_POST.ItemStarts.dateAdd(“days”, 2)}}

I tried three things:

a) Assign this binding to a $_SESSION variable, like in
Set Session Result1 = {{$_POST.ItemStarts.dateAdd(“days”, 2)}}
(I tried defining this session variable both as text and as date and the results were the same)

b) Assign this binding to a variable (don’t know if they have any special name), like in Set Value Result2 = {{$_POST.ItemStarts.dateAdd(“days”, 2)}}
(I don’t know how to specify the type of a value variable)

c) Assign this binding to a table field, as shown below:

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None of these three operations works and the server action dies. If I don’t have the “set” commands and just try to insert the record, the action doesn’t happen.

Date Diff
Let’s say that I want to know the number of days between my two dates:

Using the “formatter”, I get the following string:

{{$_POST.ItemEnds.dateDiff(“days”, $_POST.ItemStarts)}}

I tried all three of the above approaches with the same results.

Am I doing something wrong? I’m totally stuck.
This is a batch process, so I can’t pass all the values from the client side and I need those calculations done.

Many thanks in advance!!

Alex