???
If the authority fails to process the building permit (reject or approve) within a legally set deadline, the law also states that the building permit is granted as applied for or that one can build without a building permit. What this has to do with stamping - no idea. But as already indicated: the planning office should know the deadlines better.
Well, a municipality / city can impose a development freeze over an area until a development plan becomes legally binding and in the meantime stop / reject all building applications due to the development freeze.
Fortunately, this is not the case here.