How long were Muriel + David married?
The movie moves very quickly from the wedding to Muriel's mother's death, and the first time I watched it, it seemed like it was within a few days, and when Muriel and Rhonda leave Porpoise Spit together, they don't take any luggage, which makes it seem like the old apartment hasn't been let go yet and Rhonda's things are still there.
However, when Muriel tells David she can't stay married to him, she says, "good luck in the games", which would seem to indicate they had been married at least the four months he needed to qualify to compete for Australia. And after the wedding, Rhonda tells Muriel that she couldn't make it on her own in Sydney and had moved back to her mother's house.