statistics table hang

using  the below procedure,  for some days the procedure will run for max 10Min, while other days can stay all day running?

how to check what is blocking , or to investigate further the behavior?

SYS.DBMS_STATS.GATHER_TABLE_STATS(OwnName	=> 'Owner1',
	TabName	=> 'table1',
	PartName	=> 'PART_' || DAYID,
	Granularity	=> 'PARTITION',
	Estimate_Percent => 35,
	Method_Opt	=> 'FOR ALL COLUMNS SIZE AUTO',
	Degree	=> 8,
	Cascade	=> FALSE,
	No_Invalidate	=> FALSE,
	force =>true);

thanks,

Olta