Tomato transplants should after the last normal freeze/frost date in Parker County.
In spring the best dates are between March 25th and April 15th. If a late freeze/frost is perdicted cover your plants with a cloth material. Avoid using plastic material as the plant can not breath. If plastic has to be used it is best to remove it after the temperature is above 32°.
July 1st and July 25th. Water new plants thoroughly and water often until plants are established. With some protection from cold and cold wind it is very possible to have fresh tomatoes as late as Christmas day.