Nah, empty mares cost the same to run as dry mares SC.
Keep swinging at them all the way to the end of December & if you have to a bit beyond that even.
IMO imposing arbitrary dates is madness. 2yos don't know their foaling dates.
Take a few from last season for example.
Cowgirls N Indians, the winner of last season's 2yo Fillies Australasian Breeders Crown, was a 2nd of January 2009 foal.
Mr Nickel, the APG 2yo Colts & Geldings winner, was foaled on the 18th of December 2008.
Western Cullen, the WA Golden Slipper winner was a 15th of December 2008 foal.
The previous season...
Ohoka's Bondy, winner of the 2010 WA Golden Slipper, was a 5th of December 2007 foal.
Previous to that, Smiling Shard is a December 3rd, 2006 foal and he STILL holds the Australasian 2yo record of 1:53.6? if I recall the time correctly.
The reason that less later born foals are annually documented as having won the big races has nothing at all to do with them somehow being 2 or 3 months behind or less mature than their contemporaries some 2 & 1/2 to 2 & 3/4 years down the track after they were foaled...but rather it is simply the fact that statistically there are far fewer of them.
It is a function of numbers that serves to create a myth. If you look at the Bell Curve produced by foaling dates it backs that up.
In summary, I'd keep taking shots if I were you. Geeze, in the South Island of NZ I'd reckon that half the mares would still be struggling to hit a proper cycle & it doesn't stop them producing early winners.