Eleven isn't a very big number. Eleven days isn't a particularly long time. To be honest, I rarely think about time in chunks of eleven days. Seven days, yes. Thirty days, yes. Eleven days, no.
But if you want to put something off, then eleven days seems like a good span to do it for. After all, you can always do it next week and then not get around to it until Thursday or Friday.
Likewise, if you are compelled to postpone an engagement, then normally the same time next week won't do – things are pretty busy right now. Two weeks is too long, so you postpone for about eleven days.
Could eleven days be the natural length of procrastination?
I don't think so, but it's a fun idea to play with.
Yesterday happened to be the one hundred and twenty first day of the year. That means we've had eleven chances to put something off for eleven days. We only get about twenty more chances to do that.
Or to put it another way, the year is a third over. The first act, the introduction is complete. Time for action.