Maryland Code, Estates and Trusts § 5-207

(a)(1) Regardless of whether a petition for probate has been filed, a verified petition to caveat a will may be filed at any time before the expiration of 6 months following the first appointment of a personal representative under a will, even if there be a subsequent judicial probate or appointment of a personal representative.

(2) If a different will is offered subsequently for probate, a petition to caveat the later offered will may be filed at a time within the later to occur of:

(b)(1) If the petition to caveat is filed before the filing of a petition for probate, or after administrative probate, it has the effect of a request for judicial probate.

(2) If the petition to caveat is filed after judicial probate the matter shall be reopened and a new proceeding held as if only administrative probate had previously been determined.

(3) In either case described in paragraphs (1) and (2) of this subsection, the provisions of Subtitle 4 of this title apply.