Naps at a precise hour really don't matter, it's more the ritual that indicated it's time to have a nap eg the 4S's,
One of the reasons it may not work with anyone else is that he may need to tweak his own rituals that are slightly different to your's but indicate a routine. Rather than you stepping in it could be worth him trying to see if he can have a ritual & then let her sleep in his arms for a day or two & then work towards sleeping in the crib.