I worked in a call center about 5 years ago almost 6 years ago now and most times I worked 9 hours with an hour break during that time.
So I was at the call center for 9 hours with 8 hours of that time spent at the call center actually working while the other hour was used for lunch and bathroom breaks.
A few times I worked 14 hours as overtime when the call center was really busy and I got paid for that extra overtime.
The overtime usually happened during really cold or bad weather when I would be just sitting at home doing nothing anyway so it didn't matter to me if I worked overtime and earned more money.
But most times a call center employee will be in the call center from 8 to 9 hours but do expect some overtime as well during really busy times depending on the call center and company you're working for.