**Describe the unexpected behaviour**

Neither of these works:
```
now64(3, 'UTC')
now64('UTC', 3)
```
{
public:
    explicit ExecutableFunctionNow64(Field time_) : time_value(time_) {}
    String getName() const override { return "now64"; }
    ColumnPtr execute(const ColumnsWithTypeAndName &, const DataTypePtr & result_type, size_t input_rows_count) const override
    {
        return result_type->createColumnConst(input_rows_count, time_value);
    }
private:
    Field time_value;
};
class FunctionBaseNow64 : public IFunctionBaseImpl