try to use function:
intck()

Date and datetimes durations can be easily calculated by subtracting the smaller date or datetime from the larger.

将两个日期设为两个变量 直接相减就行

try this

data name;
set yourdata;
date1=mdy(substr(left(date1),5,2),substr(left(date1),7,2),substr(left(date1),1,4));
date2=mdy(substr(left(date2),5,2),substr(left(date2),7,2),substr(left(date2),1,4));
day=date2-date1;
run;

将输入格式调成yymmdd8.  然后两个变量直接相减即可