They'll be fine. I just finished my first hatch last week with a great hatch (about 90% if you don't count the 13 eggs we set that were not fertile to begin with because those hens didn't like my rooster), only one early quitter and only one that went into lock down that didn't hatch. I have a still air incubator and turn by hand. Most days I turned 3 times a day, at approximately the same time of day (within an hour), but there were some days when I could only get home to turn them twice a day. Usually I turn when I get up or right before I go to work (between 5:30 and 7am), when I come home for lunch (between 12:30 and 1:30pm, although it can be as late as 2:30 on weekends if I get busy and forget during the "lunch hour"), and again before bed (around 8:30-10pm). About once or twice a week through the whole incubation process there would be a day when I couldn't do the mid-day turning, so the eggs only got turned in the morning and about 12-14 hours later before bed. Personally, if I were in your shoes I probably wouldn't bother asking your sister to turn the eggs at 8 if you'll be turning them an hour and a half earlier, but it's a personal decision.
