You won't really get any kind of straight answer on when a new offer might come through (if at all). The threshold that it gives is when they start reviewing you to see if they will make you a new offer, how much, and when. They might wait until you pay it completely off, they might offer it right away, and they might not offer it at all. Their criteria is not public information, so best to just keep your fingers crossed and keep meeting your deadlines if your hoping for a new offer.
I just paid my 3rd off with over $1200 left to pay on it hoping to get more for the holidays. The other 2 offers came in right away after the 1st and second were paid so I thought this would as well. It has been over a week and it just keeps saying we will let you know when an offer is available. If I had known it was not a "for sure" I never would have paid the over $1200 that was left on the 3rd one, I would have invested that in inventory or marketing. Now I feel like I am out that money as I keep reading offers are not a for sure thing. One would think after 3 loans (2 of which paid early) that it would be.