For my older kids, we started "informal" college visits after 8th grade year. In most/all cases, the younger ones tagged along. As a consequence, all of them got to see/feel/etc. the environments of places like Texas, Texas A&M, SMU, TCU, UTD, etc. I recommend gettning started before junior year.
My youngest graduated HS in 2023. Because of COVID, we did not (or could not) visit any colleges from Mar'20 - May'22. As a result, he did not have a really good feel for any of the places - and a 2-day whirlwind visit of colleges will not often do the trick. He narrowed his selections to Texas A&M, Purdue, and RPI, wanting to major in CS. He did not want to go to UT. Narrowed further to Purdue and RPI (because of the way A&M handles "freshman engineering") and ultimately chose Purdue. We'll see how he likes that decision in February...
We were tried to nudge a little toward SMU (closer to home, smaller school, decent ECE program, strong Dallas area internships, etc), but he did not have the same feeling. Did not want ECE and the SMU CS dept has been a little disorganized as of late. Also, he was turned off by the fact that some of the less capable, more foolish kids from his school were going to SMU.