I have heard that the time released fertilizers (osmacote) breaks down
very quickly when it gets hot in the sun. Someone told me not to use in on
seedlings for this reason because it will burn tender young plants (not just
orchids).

Does anyone have any experience with this?

Gene,

I can tell you from my FL growing experience that osmocote and the other
time release ferts placed on top of the medium in our warm and sunny climate
don't last nearly as long as they should, so obviously the pellets are
breaking down quickly. I never use it on babies, but everyone else except
my one Paph gets it. When my husband uses it for in-ground plants he mixes
it into the soil.

Diana