How to validate elements of a list slot individually?

Within a form, I have a slot called times of type list. I want to validate that for each element of the slot, am/pm is specified. For example, if the slot is filled as [12pm, 3pm, 6], I’d want to keep 12pm and 3pm in the slot but ask the user “Did you mean 6am or 6pm?” The problem is, if I keep 12pm and 3pm saved, then the slot would be considered filled and the form would move on to the next slot.

I have several ideas for workarounds such as using a temporary slot for validation purposes, and saving only those values which pass validation to my slot times. However this is not very elegant and I’d like to know if there are better alternatives.