I was recently arrested for possession of marijuana on the UNT campus in Denton. (First offense.) How long before the court charges me? I haven't heard anything yet, but it's only been about a month.
The easy answer is two years. However, the limitations time can "toll," or be put on hold, in several instances, including if you leave the state and if the state formally files charges against you (whether you are aware of this or not).
Start looking to hire a lawyer so that if and when the state files charges, you will be aware of them and can turn yourself in on your own terms. What you do not want to happen is for the state to file charges, you not know about this, and then get picked up on a warrant in a couple of years.
This answer is based upon the limited information provided in your question, and is not intended to be legal advice, nor create an attorney-client relationship. For more information on your particular situation, please contact a local attorney.