Shift Hours Timing

Dear All,
in our organization we are having three shifts Morning General &second..
my query is for morning(6.30 to 3.30) and general (9 to 6)we are working for 9 hrs. and for second(3.30 to 12) it is 8.30 hrs.so is there any rule for second shift work for 9hrs
Please advice

for any shift timings you observe the following.
the total hours shall not exceed 8 and half hours.
the lunch hours shall not exceed 30 minutes.
except General shift, I and II shift shall not be overlapped
as per factories act.