For non-rolling admission schools, the effect you talk about is less simply because the pressure is less. I remember how some Iowa applicants who had the same interview date as I did didn't get a decision until weeks after I heard from them. For rolling admission schools, the pressure to be "early" is in the submission of applications as interview invites are awarded first-come first-served during the adcoms' periodic review of the applications.
I don't know what goes on in the mind of an adcom, but I would generally interview as early as possible simply because it allows for a decision to come earlier in the semester allowing you piece of mind during the spring semester. I suppose there is an advantage interviewing in January versus April, but not between the first and second weeks of March.