We did some very preliminary touring sophomore year (large public, smaller publics, privates). Then, we did net cost calculators like crazy fools to figure out which schools were within our budget (both my kids were given hard dollar limits we were willing to spend and told that anything beyond that was on them.....if they chose wisely, they could do it debt free). Once they knew which schools were "affordable", they each asked to tour a few for a second time, with more specific program visits. They each chose ONE to do a very early application (for decisions before Thanksgiving....which gave them time to do other applications if they did not get in to their chosen first choice). They were both accepted. Done. It does not have to be crazy. Seriously. Have them do a LOT of research about the colleges on line....there's a TON of stuff available without leaving your house. Then tour those that meet budget and program requirements.
Applications are done in the first half of their senior year, for the most part. Some a bit later.
I would encourage you first to get a handle on the cost piece. It's eye opening (and sometimes surprising) how much families are expected to contribute. Needs based aid is not available to too many folks. Scholarships can be a crap shoot. Finances can dictate pretty quickly what kind of school your kid attends, unless they want to take on debt.
We did not spend crazy amounts of time touring. My son ended up attending the U of Minnesota, where he was already enrolled as "dual enrolled" senior....so he knew EXACTLY what he was getting. My daughter narrowed her choices to two, which happened to be in the same community. We did an overnight visit and saw them both.
Our preliminary tours were done while we were on road trips, or generally in the neighborhood already.