No rush at all. Moreover, contributions made during Open presale: 24th September — 8th October give +20% bonus tokens; while contributions made on private presale (13th August — 24th September) give 25%. I believe the difference in 5% is not a big point.
Yes, but you forgot one thing-)
The special offer bonus of 10% (1 million tokens) will be available during the initial sale stage. So there are more incentives to purchase during private presale (13th August — 24th September) in order to get +25 bonus PLUS some part of 1 million of special bonus.