Lockdown is not something that has to be spot on. Eggs can pip very early or very late due to different things. The main thing is average incubating temperature, but some other things can affect when they pip and hatch. I had eggs pipping when I went into lockdown until I adjusted the temperature on my incubator. You don't always shrink-wrap chicks when you open the incubator after they pip, but it can and does happen. It's best to go into lockdown and raise the humidity before they pip. That's your real goal.
Some people have trouble counting days. There is even a hatching calendar floating around this site that was wrong the last time I looked at it. It seems like Day 1 should be the day you start the eggs, but that is not correct. An egg does not have 24 hours worth of development two seconds or two hours after it goes into the incubator. It takes 24 hours for the egg to have a day's worth of development. The day after you put them in the incubator is Day 1. That just doesn't sound right, but it is.
Lockdown should be after 18 days of development. Since you set then on Saturday March 24, lockdown should be Wednesday, April 11. Since it is your first time, I'd shoot for around 3:30 p.m., since that is the time of day you set them. When you get some history of how your incubator works, you may want to adjust that some on future hatches.
A good way to know when the eggs should hatch is that the day of the week you set them is the day of the week they should hatch, in your case, Saturday. But don't be surprised if you are a couple of days early or late. Many of us are, especially the first or second time.
