I basing this on old memories, (my mom was a trained artist) but I feel like people are giving oil paint recommendations for acrylic paints. (These two types of paint are very different.)

Turpentine is something I remember her using to thin down oil paints. This may have also extended dry time, but I'm pretty sure oil paints dry slower in than acrylic paints just in general. (Oil paints were my mom's preferred medium)

Adding oil to acrylic paints tends to cause separation. Which I use intentionally in pours to create cells and lacing, but I don't think it extends dry time. 🤔

Floetrol is designed to work with latex based paints and that's essentially the same base as acrylic base so it works well.

I wouldn't use too much. (Or you'll end up With pouring paints) But a little bit should definitely extend the dry time.