I wouldn't recommend this thursday events at Hockenheim at all. There is always a big bunch of different cars and bikes with a wide range of driver skills - you can drive for about 20 minutes then the next group comes (bikes and cars seperate) and it's usualy only on the short track - no need to drive hundreds of kilometers to take part here and risk a damage. And: You can only drive with street legal cars with license plate.
If you have a racing license you can use the special license day (monday AFAIK).
You better watch out for the full or half day events at Hockenheim from e.g. Wirtz promotion, pro-track, pistenclub, ACS or SAR (Swiss Autoracing - I was at their 2 day free practice event in Hockenheim this year on the Grand Prix track - great driving!)