You would get your points when you close. I believe the timeframe for closings on new purchases is for the September UY at this time, so It should be around September. (you can't close until the building you are purchasing for is built)
If you are planning on buying 270 or more points you might want to consider buying 150 points and then a 120 point add on (or more) to get the 100 bonus points for 2005 (if they are still available by then)