If you are talking about felony marijuana charges, the state can indict you anytime within the statute of limitations. So for felonies in Texas, this is at least 3 years.
If your attorney wants to rush things along, he could file for an examining trial and that will speed things up quite a bit. Your attorney could also file a grand jury packet to try and get them to refuse to indict you. The state cannot proceed on a felony charge without an indictment, unless you waive the requirement.
If the State has a strong case against you, there is normally a better deal to be had before indictment than after. If you have an attorney, you should be discussing these questions with him. If you do not have a lawyer, I strongly suggest you hire yourself one and would recommend you hire an attorney who is also a member of the Harris County Criminal Lawyers Association.