Baby aspirin. Really needing answers on this.

My doctor just told me to take one pill twice a da of baby aspirin 81mg. I was reading about it online about it and everyone said they only took one pill a day because too much could be harmful, should I follow what my ob suggested or alter it to what I found online? Also, when should I start it and stop it? I'm going to call the office back and ask, just thought I'd get some other insight as well. Thanks in advance!