Hi, well ive been on the pill for 4 years, and I dont use condoms and take the pill generally from between 9am-12pm. So anywhere within that three hour period, generally seems to keep things consistant. I've never been pregnant from my usage.
At first I was like you, really skeptical, but as long as you are careful then you should be fine.
Make sure you read the label on your packet but generally they say anything up to 12hours is not considered "late" but I would certainly not recommend doing that. My doctor says a 3 hours give or take is completely acceptable.