Model Hailey, the daughter of Alec's little brother Stephen Baldwin, and the "Sorry" singer announced their shock engagement in July. The pair enjoyed a brief fling at the end of 2015, and reunited in May of this year, getting engaged just two months later, not long after Justin, 24, split from his long-term on-again, off-again girlfriend Selena Gomez.
Asked about his 21-year-old niece's planned nuptials, Alec advised the youngsters not to rush into marriage.
"People who get married young, and they are very young, I want them to just spend time with each other," he told etalk. "Obviously, he in particular has this crazy superstar career."
Alec also opened up about his own priorities changed when he wed second wife Hilaria in 2012. Together they have four children; Carmen, five, Rafael, three, Leonardo, 23 months, and Romeo, three months.
The 60-year-old also shares 22-year-old daughter Ireland with his ex-wife, Kim Basinger.
"When you're married... Like right now, I'm quite a bit older than both of them but I got married recently a few years ago. And my wife and I had four kids in four and a half years. We have a lot of little kids. The thing is, all the work I do now is based on my family," he said.
"There's movies I got offered where they say 'Come leave town for five weeks. No we can't travel your family with you, we don't have that in the budget'. And I pass, because I don't want to be away from my family. And I hope that they realize that! If you want to have a successful marriage, you have to be together. You gotta stay together."