I think you have 0 chance. But it doesn't hurt to try. Typically longan trees are propagated via air layer because they are so difficult to graft or root via cutting. And seeds take forever to grow and fruit.

While it's not advisable, it is possible to grow longan from cuttings but it is very important to maintain high levels of humidity if you want them to be able to survive, and the success rate is low unless rooting hormones are used. Lychee would probably be a bit more difficult than longan, I would imagine.

I agree with the zero chance. But if you want to try, you have to follow the ways cutting are propagated.

You can't use the flower/fruit panicle and expect it to grow.

Use the new growth stem where the bark has hardened. Apply rooting hormone to the end of the bark. It has to be a very small thin stem. The new roots can't support a thick stem.

The problem why it is so difficult is that it takes several months for the roots to develop and the cutting would be dead by then.