the when the baby was 4 months he took 2 months leave. (we are in the US and he had 1 month paid, one unpaid). We had one month together all of us as a family, and then he did one month after I went back to work, when the baby was 5-6 month old. It was GREAT for him to bond with the baby like that, also great for me as a mom to know that he could figure it out. If your wife has longer leave, I would do it later, my brother (in Denmark) took leave when his kids where about 9 months - they are more fun.