A presiding judge can assign the judges of the administrative region to hold terms of court, try cases, and dispose of accumulated business for other courts. See TEX. GOV'T CODE ANN. 74.056 (Vernon 1998). When a judge is assigned, "the presiding judge shall, if it is reasonable and practicable and if time permits, give notice of the assignment to each attorney representing a party to the case that is to be heard in whole or in part by the assigned judge." TEX. GOV'T CODE ANN. 74.053(a) (Vernon 1998). This notice of assignment is optional rather than mandatory. See Tivoli Corp. v. Jewelers Mut. Ins. Co., 932 S.W.2d 704, 709 (Tex. App.-San Antonio 1996, writ denied); Turk v. First Nat'l Bank, 802 S.W.2d 264, 265 (Tex. App.-Houston [1st Dist.] 1990, writ denied). If time or other circumstances make it impractical for a presiding judge to give the parties notice of the assignment, he is not required to do so. See id. A party that complains about the failure to receive notice must show it would have been reasonable and practical for the presiding judge to send such notice. See id. If a party to the case timely files an objection to the assignment of the judge, the judge shall not hear the case. See TEX. GOV'T CODE ANN. 74.053(b) (Vernon 1998). In order to be timely, an objection to the assigned judge "must be filed before the first hearing or trial, including pretrial hearings, over which the assigned judge is to preside." See id. 74.053(c). Further, an objection to an assigned judge filed after the assigned judge makes any rulings in the case is untimely, regardless of whether the judge held a hearing in open court. See Perkins v. Groff, 936 S.W.2d 661, 666 (Tex. App.-Dallas 1996, writ denied). A party's timely objection to an assignment of a visiting judge is mandatory. See Tivoli Corp., 932 S.W.2d at 709; Turk, 802 S.W.2d at 265. Once a party makes a timely objection to an assigned judge, the assigned judge's disqualification is mandatory. Amateur Athletic Found. v. Hoffman, 893 S.W.2d 602, 602-03 (Tex. App.-Dallas 1994, no writ). An objection to an assigned judge is timely if made before the assigned judge, sitting on the bench in open court, calls the case to hearing or to trial. Id. at 603. Any order entered by the assigned judge then becomes a nullity. Id.