You have more than the day the "new moon" starts, AFAIK -- I don't believe in this new moon stuff though.
Cultures have different meanings, some cultures, the actual moonlight on a FULL moon has more healing, but the same moon turns everyone crazy mad loons in other places, apparently :)
I think we give more meaning to things than is there sometimes, but maybe others will disagree. I just signal the new moon with a chance to start as I mean to go on, the new moon is like a shorter new MONTHS resolution, one you can actually keep I suppose.
If Andreas Mortiz can't make up his mind, we have little chance.. heh