In my view the McIntosh report on overnight care by fathers for very young children (<4 yrs) has been discredited and should no longer be used.
Young children do not suffer distress or have their development affected when looked after by a loving caring father.
50/50 care is entirely appropriate where circumstances permit (ie not breast-feeding, both parents caring and supportive of infant).
Taking some selective quoting from Warshak et al:
There is no evidence to support postponing the introduction of regular and frequent involvement, including overnights, of both parents with their babies and toddlers. Maintaining children’s attachment relationships with each parent is an important consideration when developing parenting plans. The likelihood of maintaining these relationships is maximized by reducing the lengths of separations between children and each parent and by providing adequate parenting time for each parent. Such arrangements allow each parent to learn about the child’s individual needs and to hone parenting skills most appropriate for each developmental period. The optimal frequency and duration of children’s time with each parent will differ among children, depending on several factors such as their age and their parents’ circumstances, motivations, and abilities to care for the children. Other important considerations include children’s unique relationship histories with each parent and their experience of each parent’s care and involvement. In each case where it is desirable to foster the parent– child relationship, the parenting plan needs to be sensitive to the child’s needs, titrating [concentrating ? RW] the frequency, duration, and structure of contact.
If the child has to be returned within 2 hours of being picked up by the father, this leaves little time for relaxed interaction. Overnights help to reduce the tension associated with rushing to return the child, and thus potentially improve the quality and satisfaction of the contact both for the parent and child. Overnights allow the child to settle in to the father’s home, which would be more familiar to the child who regularly spends the night in the home compared with one who has only 1-hr segments in the home (allowing for transportation and preparation for the return trip). The physical spaces in which father–child interactions take place influence the nature and types of interaction, and affect the father’s identity as a parent (Marsiglio, Roy, & Fox, 2005). Nonetheless, because of the relatively few studies currently available, the limitations of these studies, and the predominance of results that indicate no direct benefit or drawback for overnights per se outside the context of other factors, we stop short of concluding that the current state of evidence supports a blanket policy or legal presumption regarding overnights. Because of the well-documented vulnerability of father– child relationships among never-married and divorced parents, and the studies that identify overnights as a protective factor associated with increased father commitment to child rearing and reduced incidence of father drop-out, and because no study demonstrates any net risk of overnights, decision makers should recognize that depriving young children of overnights with their fathers could compromise the quality of their developing relationship.
Too often mothers use parental alienation with the support of professionals, both pysch and legal, using discredited research (eg McIntosh) to reinforce their unwillingness to properly co-parent.
I accept circumstances are not always conducive to 50/50 co-parenting, but in the absence of significant mitigating circumstances, then equal time is what is best for the young child.