You cannot legally challenge a will before the testator, or the person who made it, dies. But in some states you can file a lawsuit in civil court while the testator is still alive if you believe another beneficiary has unduly influenced the will. The charge is “torturous interference with an inheritance.” Your time limit to file runs until the testator dies.
Your next option is to get to the probate court before the will does. This window of time can be anywhere from days to years, depending on when the will is found and how quickly the executor attempts to file it for probate. A "caveat" or written objection placed with the probate court prevents the will from entering probate until your challenge can be heard by a judge.
The statute of limitations for contesting a will begins running once it has been legally filed with the probate court. In most states, this is two years. This period generally begins with the date the will is accepted into probate, not the date of death.
A minor cannot file a lawsuit, including a will challenge. Most states extend the time frame for contesting a will in such cases, giving the minor two years after he has reached the age of majority to file a challenge. In 2010, the Texas Supreme Court decided that under some circumstances, the statute of limitations for contesting a will can be extended to four years from the date probate closed. This new law applies if you were unaware that you were an heir at the time the will was probated, such as if you did not know the deceased was your parent. Most states will also make exceptions when a new, more recent will is found after the first one has entered probate. If the new will is declared valid, it takes precedence over the older one. Any statute of limitations to contest it begins when the new will is filed.