Their is no rule against listing things that you did in HS on your application. If it is a one-and-done in HS and you don't continue the activity into your college years, it looks like box checking which is to be avoided. Don't think about it as "hours". Think about how the totality of your application, including the 15 items you choose to describe in your work & activities section, describes your exploration of a career in medicine, your values, your circumstances, your work experiences.
In other words, everyone is going to have shadowing and/or clinical experience that shows that you have explored medicine as a career. Your values may be demonstrated by volunteering, engagement with your faith community or other group, advocacy, other service, business development. Your circumstances might be elucidated by your work history as a non-traditional student or over summers and breaks or an "other" category that describes your responsibilities caring for a elderly or disabled family member.
In engaging in research, were you curious? Were you directed to this activity because you were a smart kid who needed enrichment of the usual academic path through HS? Were you testing a career as a bench scientist? Were you modeling the career of a physician scientist you knew, or knew of, and thus made this part of your testing of a career in medicine?
Do you have 15 other things that are more important in showing those who read your application what you have done and what it says about you?
