Do sweet dishes taste sweeter when hot or when it gets cold? While cooking something sweet which would be served cold or at room-temperature, is it more sweet when it is hot i.e. during the cooking when you taste in order to check the sweetness, or when it is served cold or at room-temperature i.e. after the cooking?

I feel that it tastes slightly less sweet when served at a lower temperature. Is that right?
Sweetness is perceived in inverse relation to temperature, so what you say is quite correct. Further along the same range, ice cream or sorbet tastes much less sweet when frozen than when you taste the initial base.