How your data is stored is entirely separate to how you choose to display it. Assuming the dates and times are meant to represent fixed points in time (rather than floating "local" times) I would try to write as much of the application as possible with DateTime
values in UTC. When you retrieve data, convert it from your "storage time zone" if you need to (you haven't said which zone your data is stored in) and convert it back when you store it. When you display it, display it in whichever time zone you need to.
You don't need to set this at a global level as far as .NET is concerned - you can have an application-wide configuration setting (if you really want to) and "helper" code to convert it whenever you need to display. I would do so very explicitly though: you really don't want conversions happening implicitly when it comes to time stuff.
(I'd also mention that my Noda Time library may come in useful as a clearer API when it comes to dates and times. I'm biased, of course. I'd also suggest migrating to storing everything in UTC if you can... and only where appropriate, of course.)
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…