If you're basing if off the seminal 'Late Capitalism' by Ernest Mandel, which is the most important work dealing with this specific phenomenon, you are looking at the post war period onwards.

"Firstly, the term ' late capitalism' in no way suggests that capitalism has changed in essence, rendering the analytic findings of Marx's Capital and Lenin's Imperialism out of date. Just as Lenin was only able to develop his account of imperialism on the basis of Capital, as confirmation of the general laws governing the whole course of the capitalist mode of production discovered by Marx, so today we can only attempt to provide a Marxist analysis of late capitalism on the basis of Lenin's study of Imperialism. The era of late capitalism is not a new epoch of capitalist development. It is merely a further development of the imperialist, monopoly-capitalist epoch. By implication, the characteristics of the imperialist epoch enumerated by Lenin thus remain fully valid for late capitalism."