nope, nobody is exaggerating. Once her scent is in the air, males will be around your yard. I have seen dogs chew through fences to get to females in heat. Do not let her outside for a second without you. I have heard of males chewing through sheetrock to get to females in heat.
As stated by others, take no chances. Not common, but not unheard of, girls being bred on day two and three of their heat and as late as day 21 and 22. Don't count on blood as being your timeline for safety. Until she is no longer swollen at all and there is no signs of blood or any color discharge, consider her able to be bred. I would take all precautions for a month.