This is a bug in Reviewer Portal as of GIFTS Online v 6.5. What is happening is that the review dates are created in ET, but when accessed in a more Western Timezone, the hour shifts back, causing the times to fall into the prior day. The dates still refer to the day you specified at midnight, the day you specified in ET, but it will fall an hour early for Central, two hours early for Mountain, etc.

There is currently no workaround for this issue, but the only affect it should have on your workflow is perhaps some confusion on your reviewer's part.