Todomomo

Ummm I'd say they dated in highschool and got married after five years. So at least seven years of dating. Maybe six? Depends on when they got together.

Kirimina

I'd say only a year after graduation.

Miruhawks

Eloped after two years of dating.

Iidamei

Four years.

Kamijirou

Maybe a year or two after graduation

Dabi x toga

I'm honestly doubting that they got married now. Probably three years after meeting each other. Dated for a year.

Nejitama

Known each other for three years. I'd say they dated for about six years, maybe had Amai before marriage, I doubt it but maybe.

Mt.Kamui

Probably a year

Ryushot

Dated for about two years, we're engaged for only a few months, and got married.

Reiko x Shinsou

About four years.