Both sunflower oil and olive oil are good cooking oils for making roast potatoes.
I personally prefer to use olive oil when making roast potatoes but the sunflower oil makes good roast potatoes as well.
Depending on how many roast potatoes you're making it can take between 30 minutes to as long as 2 hours to make roast potatoes.
You can also use any type of vegetable or cooking oil to make the roast potatoes with and they will turn out just fine.
But I prefer the olive oil for roast potatoes as well as making french fries or just frying potatoes in general.