Hi James,
R&D confirmed it is an issue, they never said if it's by design or not though.
Incident 266084 / 2016 / DateTime field is rounding up now in CR .NET
2310683 - DateTime field is rounding up now in Crystal Reports for Visual Studio SP 15 and above
Unfortunately SP 17 is closed so we have to wait for SP 18 in September.
Thanks again
Don