This deviates from the other code here which simply passes the values through (except for date parsing). I wasn't sure if we should be trying to do any clean-up at this point, or if there's a better place for it.

The attribute "institutionSpecified" is meaningless to me, and seems counterintuitive at best. The meaning (according to http://ushik.ahrq.gov/ViewItemDetails?system=hitsp&itemKey=83185000, which had one of the better explanations) seems pretty straightforward.
Consider a period of 6 hours. An "interval" schedule should actually be done every 6 hours (midnight, 6am, etc). A frequency schedule should be done 4 times per day, but 8am, 12pm, 4pm, 8pm would be fine.
I thought translating it here would be an improvement, but I understand if that's not the role of this library and you'd rather leave it up to the developers to make sense of the results.