The reason why (I think) this was less likely to work was because of haste. The hackers knew their tweets would be pulled down in a few minutes or so, so they

The reason why (I think) this was less likely to work was because of haste. The hackers knew their tweets would be pulled down in a few minutes or so, so they had to put out tweets saying "in the next 30 mins" for people to send money immediately. This works well in what they tried, but asking people to donate in the next 30 mins would certainly have made it look suspicious.