A will can be changed at any time before death if a person is competent. The changes should not be made by alteration to the existing will but by a document called a "codicil". The codicil must be executed with the same formalities as a will.
Ideally, you should be able to close the estate within 13 months of the decedent's death. However, depending on the size and complexity of the estate, it may take longer. In any case, it's important to keep meticulous records throughout the process to prove to the court that you've fulfilled all your fiduciary duties.
Contesting a Maryland will can be a complicated process. A will contest is often done through a caveat proceeding. There is a time for a caveat proceeding after ? it is usually six months ? an estate is opened, then that will can be caveated. A caveat or the challenge can be served for any number of reasons.
Also, the petition challenging a Will in Maryland generally must be filed within 6 months of the first appointment of a personal representative under the Will. This is a short statute of limitations with serious consequences.
If the testator was suffering from some sort of mental impairment (e.g. Alzheimer's, dementia, or a delusion) at the time the will was created, the will could be invalidated. Forgery or Fraud. If the will was completely forged or the testator was tricked into the signing the will, it may be invalidated. Duress.
In Maryland, a no-contest clause is valid and enforceable only if there is no probable cause for contesting a will or instituting other proceedings relating to the estate. Similarly, in the District of Columbia, a no-contest clause is enforced without regard to probable cause.