I agree with pp saying you have plenty of time. Our party last year sold out the day of I think. I have the impression the sold out parties sell out just beforehand. We bought in oct last year and then bought two more tickets a few weeks later. We had not even planned to go until then.
We will be going to one of the more popular parties this year but haven't even thought about buying tickets. You should be fine waiting at least into sept/oct. I think someone posted a chart for you. Take a look at that and get an idea. Have fun!
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