Do you know how much longer I can expect for each?
Nope, sorry. It would be a guess at best, since they can also look even bigger when they've eaten a lot, and I've seen females that look huge and ready to pop hang on for ages, and other females who barely looked gravid pop out 20 fry!
Usually when you see the gravid spot get quite a bit darker and larger, and when the female gets a sort of square shaped "boxy" look, they're getting ready to give birth, so in the next 24-36 hours or so, usually. But not always the same for every female.
It won't be long before you have fry though, so don't worry on that account. If you're worried about exactly when, is that because you're planning to move the females before they give birth? Because I'd recommend avoiding that if possible. Moving them causes stress, and stress is very bad for any pregnant or labouring female, of any species! Can result in labour problems and fry loss. Those breeder boxes can really stress out a female too.
Better to add a lot of floating and dense plant matter to the tank, as this creates a safe area for the fry to hide from the adults, and for her to give birth. Then check often for fry, and can gently catch the fry and move them to a breeder box or nursery tank to raise them away from the adults.