In her "thank you" message to the people of New Hampshire for their warmth and courtesy Palin said "we will see you again soon". It would seem possible that when she does see them again soon it will be as a candidate or she will declare in New Hampshire.
There are a number of auspicious days in September e.g. Constitution Day, which might be suitable and there are days that if she declares she could participate in a debate with other candidates. She also said she would declare on the local Bob & Mark radio show-in which case a Friday might be auspicious for weekend media coverage.
Here's what top pundit Stacy McCain thinks:
Stacy McCain, at The Other McCain:
“Palin has specified September as her deadline for making a decision, and there are three debates in September — Wednesday at the Reagan Library in California, Sept. 12 in Tampa and Sept. 22 in Orlando. If Perry underperforms in those debates, Palin may see the front-runner’s weakness as an invitation to enter the race.”
See if you can pick the date, and how many others get it right. The only prize will be self satisfaction at being a seer and, if you leave your reason for your choice in the comments section I will re-publish this with the winners names for you to bask in your punditry!