When I pot plants up, I would like to have a minimum of a week. This I would hope would give the plant time to adjust to their new temporary home after being disturbed. Plants seem to wilt a bit for a day or so after digging them up and putting them in a pot. I don't really have a maximum amount of time. My thoughts on this is just my opinion and a bit of experience when potting up plants. I try to use store bought soil too, so they get a bit more nutrients to help them out.

For plants for sale- or when it is important for them to be healthy looking in their pots, I too like to give a week or 2 minimum- I like to see new growth or some sign of fortitude and vigor before the sale.
Some plants do not need that much time- like sedum-
Other's may need more time- or will take longer to "perk up" and look healthy- especially if they are too cold- too wet- too dry- ect-
The maximum? Well, I have a few still in their pots from last year that already look favorable... Time will tell. I would hazard a guess- that if the pot holds up, and the plant is healthy it could stay there it's whole life.
As far as dirt goes- I feel, If the plant is growing well in my yard- and will continue to grow well in my yard dirt- even if in a pot- why not use my yard dirt, except it is very heavy and requires a lot of work to dig up and sift out roots and rocks and such... and then there are the holes left where it was removed from..... Compost from the bin is a bit easier- Some plants require specific requirements.... Although, I believe that seedlings do better in Miracle grow- and I will probably always use that for them.
When I have brought plants home- I have sometimes marveled at what comes out of the pot at transplant time! Some times clay- sometimes store bought- sometimes almost all sand!! The best finds in the dirt have been marbles, buttons and cupboard knobs!! One pot stands out in my memory- it came from afar through the mail, and when I opened the box- I was flooded of childhood memories of my Aunties place near Puget Sound- the smell of the ocean was so embedded in the soil the plant came in. I was quite stirred.
I have brought fresh dug (weather and season appropriate), bare root bulbs, perennials and shrubs/trees to swaps, unrooted fresh cuttings too - and, unless I bring way too many, or they really were not that desirable (Garden Phlox in HUGE bags) usually they do become adopted and are whisked away to new homes.
I think it is all a matter of individual preference, and situational variances. How will you feel about what you are offering. Are you just unloading unwanteds by the bag full (like my Garden Phlox)- your attempts at hardwood cuttings the same year your made them (risky, for me that is)- or are you staking yours or another's reputation on quality plants. For me, it all has some thought and bearing involved. And well- time and energy level too... or lack there of....

Ramble ramble ramble....
Julie