i know mine will put out a lot of new growth
and if the soil isnt moist, several hours of sun and heat will burn or even kill
some of that new growth.
i have a large plant in a 7gal container
and a smaller plant in ground.
They were both planted from seed at the same time
but the smaller one is shaded much of the day (it gets about 4 to 5 hours of sun)
ive not seen the smaller one in-ground loose any new leaves due to water/heat
it happens on a regular basis to the larger one (needs to be re-potted, or planted-out)
Ive noticed chemical fertilizers, even organic ones, can add to that heat stress.
also, from what i gather, Lychee roots are particularly sensitive to heat
black containers in the direct sun are probably not a good idea..
The Longan i have really took off after i started adding a lot of leaves and mulch
(green and brown)