"It would be really helpful if posters who are saying they couldn't personally leave children of this age would disclose honestly whether their partners (if male) feel the same way."
I wouldn't leave a 3 months old overnight, even with DH.
But he would leave our 3 month old with me, if I was happy for him to be away overnight.
That's because at 3 months I am still their primary caregiver and they are more attached to me than either their father or other regular caregivers.
Both DH and I would probably leave a 22 month old overnight, but neither of us would leave a child that age for more than one night with anyone other than the other parent.
I would leave a child of that age for far longer than that (and in fact will be doing soon) if they were with DH. At 3 months, I'm the primary attachment. By 12 months or so, he's a pretty close second.
I don't think it is sexist to think that babies feel safer and happier with their mothers around. In fact I think the attempt to deny the importance of a mother's bond with her baby and the baby's dependence on her can be sexist.
For example, I would argue very strongly that a 3 month old baby should not have to be made available for overnight visits even with his own father, if the parents were separated. I think part of feminism is recognising and celebrating what women can do with their bodies and what that means for them and the babies they create.
I think it is absolutely fine to leave your children with other people if you want or need some time away from them. But trying to justify that by saying that babies don't notice when the person they are with 24/7 just vanishes from their life is silly.