I'd probably do a dollar cost averaging, though April 1 isn't that far away. That's about 10 weeks, so I'd divide the amount I had into 10 and do 1/10 each week, assuming you don't pay a fee per exchange.
That said, make sure you research where to do the exchange. Getting a good rate is going to be critical, and IME, US banks are terrible. When I had yen I wanted to exchange for Euros, I was better off at the airport exchange booths, which are terrible themselves, than going to Chase. Even even for USD to EUR, I do better at an ATM than I do at a US bank. I'm sure the amounts you are looking at are far beyond what you can get from an ATM in a short time, but the point about rates stands.