When you paint the sunset in Autumn you don’t have to wait for it towards 10 in the evening, like you’ll do in Summer, and this is easier. You’ll have more energy to paint it around 5 or 6 PM. Though it’s always a slight bigger hurdle (for me) than painting the sunrise because of energy, evening time versus morning time.
A red sun. It is the best. And it can only happen when there is a thicker atmosphere.
If you have clear blue skies only, you will not get a red sun, but a yellow one. So I most often pick the more cloudy days and then I hope to still be able to see the sun, either through the clouds or shining over or under it.
After the sun has gone down fully you’ll still have about 40 minutes of light, so you can finish your painting. Take out parts that do not work, soften edges, harmonise the painting.
You'll have to take the risk: 'ending up with nothing' to get something down. Sometimes it will work out, and sometimes not. "Just by trying you'll succeed!"