When will a trial court make a decision on initial custody determinations under the changed circumstance rule?

When a trial court makes an initial custody determination, it has "`"the widest discretion to choose a parenting plan that is in the best interest of the child." [Citation.] It must look to all the circumstances bearing on the best interest of the minor child. [Citation.]' [Citation.]" (In re Marriage of LaMusga (2004) 32 Cal.4th 1072, 1087 (LaMusga), italics omitted; Burchard v. Garay, supra, 42 Cal.3d 531, 535.) The considerations and interests in both initial custody determinations and "change of circumstances" custody matters are closely interrelated. (Burgess, supra, 13 Cal.4th 25, 37, fn. 8; 7501.) "`The [changed circumstance] rule requires that one identify a prior custody decision based upon circumstances then existing which rendered that decision in the best interest of the child. The court can then inquire whether alleged new circumstances represent a significant change from preexisting circumstances, requiring reevaluation of the child's custody.' [Citation.]" (Burgess, supra, at p. 37.)