Is the paint dry?
Of course you can sell anytime you want. I can't think of a reason to prevent you, but obviously buying a house is a little like buying a new car off the lot. A car loses value as soon as you drive off the lot. A newly built house will likely sell for exactly the same prices that other new construction in the same neighborhood are selling for.
This means you might not make any money and would likely have to bring money to the closing if you sell immediately after buying, because there are transaction costs.
The good news is that while the market is not rising rapidly, it is firmer now than it has been in a couple of years, and the market markedly improves as warmer weather rolls in. With the tax credit set to expire on deals made after May 1, there will be some pressure to purchase up until April 30.
So, if you're going to wait until the market value is high enough to cover your transaction costs, you will probably miss out on the tax credit rush. Immediately after the rush, prices will soften, unless the economy turns on a dime (unlikely). Overall Dallas has experienced a stable market with some areas rising in price perhaps 5% and others dropping by 5% or more.
Waiting will also incur holding costs for you. Taxes, insurance and maintenance will eat away at your net proceeds until the house is sold, unless you find someone to occupy and pay you something. A rental is one way to bring in money while you wait for the market price to rise above your costs. You could also consider offering seller-financing terms with some added risk to you that you might wind up getting the house back should the buyer default. This choice may motivate the buyer to chase after the tax credit. A final choice (besides living in it until a year or so passes) is to try to create a lease contract that gives the renter an incentive to buy.