I have always spent more time with my single fosters than with my pairs, but even so I don't think it can ever really be enough - that's why I'd always advocate single bunnies to be house bunnies...with the best will in the world, especially in winter, they're going to be on their own for 22+ hours a day, whereas at least if they are housebunnies they can interact with the general comings and goings of the household rather than only for time deliberately spent with htem.