I'm terrible with numbers...I just cheat.
If I knew exactly which days she starting laying I could give you a better idea. You said you noticed her getting big on 9/17, so just by following what MY hen did, I'm just guessing that she laid her first egg around, maybe, 9/23. Her 2nd egg would be laid 2 days later (again, not set in stone, just a guess) so 9/25. Now, if this is correct, according to a chart I'm going to post in a link at the end of this, if she starting sitting after the 2nd egg, the first should hatch 10/13, the second the next day and every other day after that. Obviously, I could be a little off on this.
And if I didn't mention it already, this is the first clutch my birds have had so I am by no means experienced, I just did a lot of reading. If you can peek into the box everyday, that would be a good idea.
The link I'm giving you is hatching dates, but once the first hatches, the rest should hatch every couple days if they're all fertile. This link is also at a website about parakeets..there's a breeding section where you can get all sorts of answers. There's a breeding journal section and I have my birds in there, Gin and Tonic. Go do a bunch of reading at this site cause there's lots of things that you will want to know.
By the way, what are you feeding the parents? They'll need a ton of extra food, including egg food and veggies.
http://www.talkbudgies.com/showthread.php?t=14425
