It sounds like this is a felony DWI charge (which happens where a person has two or more prior convictions or has someone under 15 in the car when arrested for DWI). Texas law gives the prosecutors three years from the date of the incident to secure an indictment (Texas Code of Criminal Procedure 12.01). They cannot get a continuance on this time limit but the limit may be tolled (that is, paused) if certain actions are taken by the defendant (usually, the filing of certain motions).
You should speak with a local criminal defense attorney to clarify these questions.
Disclaimer: This answer is provided as a public service and as a general response to a general question, it is not meant, and should not be relied upon as specific legal advice, nor does it create an attorney-client relationship.