I think I know the answer to this, but need some validation.
I have several cuttings in clear cups that are almost ready for the 1 gallon pot.  Some are producing lots of leaves and outgrowing the bin, but when I remove the tote cover for a couple of hours, some of the leaves wilt, telling me they still need high humidity.  Cups are almost root bound. 
On the other hand, I've had some plants not affected by the lower humidity when suddenly moved outside the bin, and they show no stress in 65 degree, dry air environment.
So for the more sensitive plants, does this mean I need to slowly remove humidity over a couple of weeks in order to have the plant acclimate better?  Or does the root development need to be stronger to support the top growth?  Based on your experience, what do you suggest?  Thanks!

Frank...I know that one of our members uses large thin mil. plastic bags to continue the humidity effect after the cuttings have out grown the bins.  In my case, I use 24oz clear plastic cups as humidity domes, and when the leaves start crowding against the domes I simply remove the covers altogether and start a process of misting the leaves with a spray bottle 3 times a day.  Of course I am retired and therefore have the time during the day to do such tasks.  For those who do not have that luxury, I recomend the bags as mentioned above...from what I understand they also help greatly with the control of the dreaded fungus gnat.

I keep them on top of deep humidity trays ( type used for orchids) below the grow lights so it creates a localized zone of humidity that seems to help. I do mist in the morning and when I get home from work.

Frank,

You are assuming right if they have lots of roots. You essentially need to harden them off to the dryer air outside of the dome. Take them out for say 15 minutes or however long it takes to make the leaves droop. Then put them back. A few hours later do it again, assuming they have recovered well from the previous exposure. Every day you should be able to increase the out-of-dome time by at least 15 minutes. After a few days you can likely start to double the outside times, and before you know it they'll be free.

Frank,
Looks like you got good advise. I will add that I usually start exposing my plants to more air and less humidity starting at leaf #2. I then up pot them into fafard #52 soil mix in 1 gallon pots. I used to loose plants at this stage but using this soil mix changed that and I haven't lost a single plant this year. I don't need to do anything about the humidity - I just need to make sure the soil doesn't dry out. I used to add more perlite but the last 50 I did I just used the soil mix right out of the bag. I'm about to up pot a bunch of plants with less developed root systems so I'll add a bit of perlite, but I've had great success with this mix.
mgg

maybe your temperature is cold?

maybe the air is too cold and humidity is not there too......

Thank you all for the suggestions.  It's definitely getting crowded in the bin and I need to transition them to a larger area.  Much appreciated for the great tips!

like you said, some are better suited for moving out of humidity faster than the others. i lost what seems to be very hardy cuttings due to moving them out too quickly. on the other hand, few i left out to die are actually doing very well. others i left in the garage without the leaves are actually doing so well, i'm starting to wonder what is going on.

typically the cuttings in the cup should be moved to outside of the bin slowly. at this point, most of my cuttings will survive out of humidity bin for about a day or more without problem. but i'm still considering keeping them in there until the garage night temp is above 50, or i can move them to outside.

Thanks Pete.  With over 100 cuttings I have going, I have learned so much.  The #1 thing I've learned is they're unpredictable!
Before I started, I didn't know how good my rooting rate would be in the sp moss, but turns out, they ALL rooted and made it to clear cups.
I have a few in my 55 degree garage (overflow area) and they're in a bin with a cover.  These are the extras that I can do without, yet don't want to throw away.  Kind of an experiment to see how tolerant they are of the colder environment.  After a few days, some of the leaves have drooped/wilted while some are just as happy as they were in their comfortable warmer environment.