amelia, un tiempo estupendo significa que el día esta soleado, luminoso,agradable, maravilloso, que es un día que alegra nuestras vidas

the weather is nice 天气很好

Hello Amelia, "Estupendo" ( not estupento) means marvelous , splendid or great not just good. "hacer" here means "it is " The sentence means: "The weather is great (splendid)" " It is a great ( splendid)weather" or " The weather is good " would be literally " hace buen tiempo".