**Describe the unexpected behaviour**

Neither of these works:
```
now64(3, 'UTC')
now64('UTC', 3)
```
{
public:
    explicit FunctionBaseNow64(Field time_, DataTypePtr return_type_) : time_value(time_), return_type(return_type_) {}
    String getName() const override { return "now64"; }
    const DataTypes & getArgumentTypes() const override
    {
        static const DataTypes argument_types;
        return argument_types;
    }
    const DataTypePtr & getResultType() const override
    {
        return return_type;
    }
    ExecutableFunctionImplPtr prepare(const ColumnsWithTypeAndName &) const override
    {
        return std::make_unique<ExecutableFunctionNow64>(time_value);
    }
    bool isDeterministic() const override { return false; }
    bool isDeterministicInScopeOfQuery() const override { return true; }
private:
    Field time_value;
    DataTypePtr return_type;
};
class Now64OverloadResolver : public IFunctionOverloadResolverImpl