OK, so in addition to the sort within day, you also need to sort the main grid by "oldest" in the "sort by" drop down menu at the top of the grid. This should do what you want.

There are some other organizational things you could do to break up your photos into projects. One would be to create Albums for each slideshow in the Organizer. In Albums, you can click and drag the images into whatever order you want. However, in order for this to work, you have to first select an album and then change the sort by order at the top of the grid to (you guessed it
) "Album Order".

As for working with other programs, I believe my experience has been mixed in terms of whether and how they accept images from the Organizer (by click and drag) in the Organizer's selected sort order.
If you are looking for a new slideshow program, I recommend Elements 2019 which is different than Elements 14 and has a really nice and simple slideshow feature. You can try it for a 30 day trial to see if you like it.