The default value changed from 86400 to 1200. See the complete list of filters here . See this bboard thread. This was implemented ACS wide. The upgrade script from ACS 4.0 does not convert the aforementioned tables into index organized tables.
Bitmap indexes store the rowids associated with a key value as a bitmap.
Each bit in the bitmap corresponds to a possible rowid, and if the bit is set, it means that the row with the corresponding rowid contains the key value. That parameter controls how many values of the sequence are preallocated and kept in memory by Oracle.