Once you've defined your variable as "Load time column" the SCD2 loader will populate it for all cases (update, insert - SCD1, SCD2 and mixed loading).
The value used to populate the "Load time column" is actually not &sysdate but a string based on &sysdate and &systime and stored in a macrovar with name &etls_loadtime.
If you look into the generated code of the SCD2 loader you will find something like this: update_dt = input("&etls_loadtime", datetime20.);
If your SAS coding level is good enough then it's worth taking the time and try to understand the generated code. It helps a lot to understand what's going on behind the scene if you have to debug a problem - and as some code parts are rather advanced there is also a lot to learn.