I'd say after you've graduated and have had a job for a year or two at least, cus that way, you give yourself time to properly grow as a person/adult and you see the world and you are properly independent and more mature then. You've seen what the world is like and finance wouldn't be a problem and you know what you want out of life by then, since at uni you're all still wondering what it is you want from your future. I'd say a relationship should ideally last anything between a year to 3 years before the couple should realistically consider marriage. Of course there're marriages that last 50 years even though they married within a month of knowing each other, but those are rare. And risks of divorce is higher when you marry so soon. If the person is meant for you to marry, then you're meant to spend all your life with them anyway, so what's with the rush? Why not wait to make sure? Of course, how long you wait would have to depend on how old you are. At my age - 19 - I'd wanna date a guy like a few years before I get into marriage - preferrably after graduation at the soonest. But then if I were 28, I'd probably only date a man for a year before thinking about it since by then we'd both have had enough experience in life etc and would both know what it is we're lookinf for.
But ultimately, it depends on the couple - their age and maturity and if they're both ready.