No builder guarantee to finish building work in a certain date. So if you like the house, you may just wait.
If the house does not finsh after a longer time than normally do, you may ask refund earnest money and cancel the contract. Or ask the builder pay your loss (mortgage rate lock extention, long term lock, etc.)
Example if most house in the same area are builder in 5 month and yours does not finish in 7 month.