The differences between 生日 and 生辰
生辰 can mean either "birthday"(the day one's birth) or 生日+时辰 (birthday + birth time) as in the phrase 生辰八字. 

Usually, 生辰 just means birthday, but it's more literary. You can probably only see it's used in a book. For example, 而这一日子恰逢其80岁生辰. Normally, people just use 生日 in spoken, but you can say 生辰 when you try to be more literary. 

生天 isn't a correct word for birthday. 生天 in old Chinese is the same as 升天, which means go to heaven.