It will probably be fine. Silkies may hatch a little earlier (a day or so), or they might not. A day's difference is not a big deal. 2-3 days will get a bit awkward but some hens can manage it. More than that is usually a problem.
A chick can go 2-3 days without eating or drinking (because it absorbs the yolk just before it hatches, so the first chicks will be OK while waiting for the slowpokes). But chicks often like to eat & drink sooner than that.
In about 3 weeks, if there is a hatched chick but an unhatched egg as well, you can put the food and water really close to the nest for a few days. That will let the chick pop out to eat and drink, while the hen keeps the slower egg warm to (hopefully) help it hatch. (It is generally good for the hen to get off the nest to eat/drink/poop/exercise, but the chick will want to eat more frequently. You would hope to keep the hen from walking away with the hatched chick and never coming back to the eggs.)
Or you can get an incubator, and if the hen leaves the nest with chicks, you can put any remaining eggs in the incubator for a few more days.
It will probably not be a big deal. I am just mentioning ideas now, so you can think ahead if you want to. Things like "get an incubator" are hard to do at the last minute. If you think now, you can decide whether you want an incubator or not, do any research you want, and still have time to actually buy it if you decided to. (I probably would not buy an incubator in this case, unless you happen to want one anyway.)
