I need the software RTC to do some other stuff in the background,
What background? The Arduino is a single process system. There is no "background".
i took the Subsecond-Information,
do a little delay with that
How is that better than doing nothing if it isn't time. Hint: it ISN'T.
It would be awesome when there would be a library similar to the Time.h, but also with a Subsecond
parameter...
The Time library keeps track of time to better than one second resolution. It simply has no method to report that. So, add one.