When did/when will you start maternity leave?

I am currently only 21 weeks, but starting to think about when I'll take maternity leave. I know a lot of women can and do work up to their due date- go mamas! I work as a nanny and finances aren't really an issue, but I would like to have a solid savings. I'll be a stay at home mom once baby is born. 
I'm thinking of starting my leave at 30 weeks. Thinking that will give me enough time to prepare for baby and relax. 
I'm interested to hear about when you took leave. If it was later, were you exhausted? If it was earlier, were you bored with too much time off?