Since it was never actually shown for obvious reasons we can only use the variations of "implied". It would be stupid to assume i.e. the Dibneys did not do it back in the ... 50ys? 60ys? When Ralph married Sue.
As the OP said, after he married
That was between late 90ys and earliest 20ks. To lazy to dig out the wedding album for the exact date though :/
Although now that I think about it there might have been a few times before that too; but probably not before engagement.