Birth Control Question

I was wondering how exact it is when they say to take birth control at the same time. I take it within a two hour timespan which my mom (a nurse) said would be fine. I've read anywhere up to a 4 hour timespan is ok, but I've also read not to exceed 24 hours between pills. I'm taking lo loestrine fe, and I'm worried I let too much time pass and may be pregnant. I've experienced some spotting and cramping but that may just be from the pill.