So, 8th of december is the best day to create new account, make 14 posts, next day make 14 more posts and receive activity 28 in two days?
Next period starts on Dec 09 10:13:20 GMT.
So yes, you can create an account and make some posts before that, and make some more posts after that time to get 28 activity within a few hours.
But no, it is better to create a new account now. You can get 28 activity with the same way, but you don't need to post in a rush.
See https://bitcointalksearch.org/topic/til-activity-does-not-work-on-precisely-2-week-intervals-interval-timings-582736 for future period timings.
~~MZ~~