Microsoft made asctime "conformant" in Visual Studio 2015. Current versions have the expected space padding.

https://learn.microsoft.com/en-us/cpp/porting/visual-cpp-change-history-2003-2015?view=msvc-140

To avoid confusion use a current version of VC++

Or if you have issues consuming the output after re-compiling in a current version (as I did recently), make sure any external processes that parse the generated dates, are updated to expect the actual format.