> Should this be possible?
The format property in Designer has historically not been used. It's original intent may have been for situations like this, but I'm not sure.
> Do I need to set something else?
The simplest thing is to add a view layer with the appropriate parseTimestamp. However that may perform the way you want as we can't generally invert "parseTimestamp(col, format) = timestamp literal" into "col = string literal" due to the laxness of the parsing logic in parseTimestamp.
So enhancements could be to support the format property in excel - or more generally add an argument to parseTimestamp such that it preforms only strict parsing such that it can be inverted.