usually they can deal with some temperature fluctuation and some people even incubate in the 60s for the longest possible incubation time. i would be much more concerned if the heat had jumped up too high rather than having it go a little low. you should be okay but do keep in mind that the first eggs a female lays are often infertile, so if they turn out to be duds that is likely the reason why.

you can try candling them to see if they are fertile. soon after they are laid you should be able to see a pink "cheerio" in the egg. after about a week the entire egg should look pinkish on the inside. if it looks all yellow instead the egg is most likely not fertile, but you should incubate it anyhow just in case.