My calendar shows different times on different devices

My wife and I share a common calendar via I-Cloud on four devices, Apple (I Pod, I Pad, and I Mac) and one non-Apple tablet (Surface 2). We are just noticing after months of it being fine that on some devices the times are 2-5 hours ahead or behind of the same appointment on the other devices (with no consistent pattern to the degree of difference that I can see), and the same device that shows some events earlier than they were entered or show on the other devices may show other events later than the other devices, so it is not consistent by machine. Make a correction and it changes all of them, until restart then the times appear to change...any thoughts? I was thinking something to do with time zone but that would at least be consistently behind or ahead on the same machine I would think.