Oliver, good question. We should add that to our "Databases" section in Chart Expirations dialog; I'll put that on the todo list.
Here is a workaround: TFRs are updated in the same pass as METAR data, so if those are current, so are TFRs. In the current production version you can switch to weather mode, if you have METAR data than TFRs ares also current.