Just so you know, I trust local breeders on keeping their bettas healthy - because they may suffer big losses if they don't. . . . I'm talking about losing hundreds of bettas. The only thing I'm never sure of is that many of these breeders keep their bettas in slightly salted water which is actually bad for them in the long run. In short, I hardly ever quarantine unless shipping takes more than 2 days (water prams will be bad). Slow acclimation will suffice.
This is just me. I'm not saying this is the correct way of doing it.
The purpose of quarantine is to reduce or eliminate possible disease spreading. Your females have been in quarantine for 3 weeks and show no infection, thus it is safe to say that they are free from diseases. If by chance they get sick later, it is due to a new infection or caught from the new tank (their new home). Quarantine time does not restart after each shipment - specially when they go through : quarantine - ship - quarantine . . . .
Remember, if the females are now in their own solitary, they will fight for dominance once placed in one tank. Each bite MIGHT cause infection. So IMO it would be best to put them together now while you can monitor them and medicate if needed, rather than later and you can't monitor them at all.
aokashi let me know that you're probably the person to ask about this:
Basically, I bought some female bettas from aquabid and I'm just wondering how long they should be in quarantine before I can put them into the tank. They were with catwoman in ontario for two weeks under quarantine before she sent them to me and they've been with me for a little over a week now under quarantine as well. I have a thread about it in the betta fish care section on the second page if you wanted to check it out. Thank you :)