Welcome to the wonderful and sometimes maddening world of Silverudd's Blue (Isbar)!
You may be able to get an idea of the sex of your babies by the first month, usually it is a bit longer though. I have some hatched 6 days ago and can make guesses based on stance, but they are only guesses. I like it when a cockerel shows himself quickly and many SB do. There are some though... I have a little splash I was sure was female who just started growing waddles. He is 3 months old. Little stinker! He is in with several dominant cockerels though.
Thanks for the fast response! In the brooder, the splash is all of the sudden looking like s/he woke up with a different "alertness" and strut. Mainly praying that the little dark one is a female because my 3 year old is in LOVE and I can only have so many roosters. I will keep a watch! They are just precious!!