This is probably not really true.

You wouldn't be publishing patient visits publically, the only folks that'd legitimatly see that record would be those which access to that visit, and they'd most likely need to know the time of said visit. This access should be controlled via AuthN, AuthZ and audited.

You'd also generally do a lot of time-based lookups on this data; what visits do I have today, this week, and so on. You might also want an additional DateTime field for timezones and offsets, but the v7 is probably better than v4 for this usecase.