I would check the map on USPS for the map of Priority mail. If you are in the 1 day zone then I would most likely count on them arriving today.
If IDEAL said they were shipped out yesterday, then they probably were.
I think IDEAL has info on their site about the shipping:
AIR PARCEL POST (PRIORITY MAIL)
Chicks can be safely shipped to all states and Puerto Rico by Air Parcel Post. For shipments to Texas (except zips 798-799), Arkansas, Kansas, Louisiana, Oklahoma, and Missouri except zips 620 thru 635, there is no air parcel post charge. For all other states and zip codes add 20¢ per Chick, Bantam, Chukar,or Guinea, 25¢ per Turkey Poult or Duckling, and 32¢ per Gosling
So if you look on the USPS website and put in your zip and IDEALs zip code then it should have a map of how long Priority mail shipping usually takes.
If it says 1 day then you should plan on it arriving today.
Also note for future reference:
I signed up for USPS informed delivery through the website, so even if I don't have the tracking number it tells me that I have packages arriving, and shows me images of my mail pieces (not the packages of course) I will be receiving later that day.
It was through the USPS website, and all you have to do is open a free account, answer some questions to verify your identity, and go from there.
It has been really helpful so far.
Good luck!!