These types of questions typically don't get answers from Esri staff. If they do get a response, it is usually fairly general and not as or more specific than month.
Looking at the ArcGIS for Desktop Product Life Cycle Support Status document gives some insight:
There has been a bit of slippage each year with the spring releases. Looking at the trend above, I would guess sometime mid-June. That said, I think Dan's answer is the most certain, i.e., before UC.