Ok, I just lost an entire post somehow.
So I'm going to be "quick" in responding this time. (riiiiiight)
The whole purpose of the bag is to increase humidity. If the roots can't uptake enough water, they can't keep the leaves hydrated, and the leaves will droop as they release water. Adding the bag forces moisture to stay in the area around the plant, putting more water in the air around the leaves, thus preventing water loss.
If your roots are in good shape, not broken, and there are plenty of them, you shouldn't need the bag. If you want to see if you still need the bag, remove it. Check the leaves every 3-4 hours. If you see excessive leaf droop, put the bag back on! Keep an eye on it for a day or two. Especially watch for leaf droop after transplanting young cuttings, and if you see significant droop, don't be afraid to put your new transplants into a sealed bin or under a bag for a few days while they recover.
This is my understanding of it, at least.
When I talk about when to go from indirect to filtered to unfiltered light ... I want to show you what I do and how I feel like it's time. This is just my suggestion. I could be totally full of crap. Just keep this in mind. I'm only sharing what I've had luck with.
I look for three things in my leaves:
1) How translucent are they?
2) What shade of green/yellow are they?
3) How shiny are they?
Young leaves are almost like film, you can see light right through them, they're stiff, thick and small, smooth and really shiny a lot of the time. Here is an example - notice how the light just passes right through them and they almost have a sheen to the surface.

When my leaves get to this point, I will either give them several hours of filtered indoor light or 1-2 hours of direct indoor light.
To me, when a leaf matures in newly rooted cuttings, it isn't about size, it's about how opaque it is and how rough/flat (not shiny) it looks and feels. Lots of chlorophyll in the leaves makes a dark, dark green leaf, really opaque. When my leaves get dark, dark green and I can no longer see through them, they go to direct indoor light. This is what I want to see in a "mature" "full grown" leaf:


To prevent leaf schorch, I go through a similar process outdoors just like you would when 'hardening off' veggies. I give them an hour or two of direct outdoor sunlight per day and gradually increase it OR I keep them in a spot that gets a couple hours of morning sun, and afternoon/evening shade, and gradually move them out to get more and more sun each day.
Outdoor sunlight is much more aggressive. Most modern windows in houses are treated with some kind of UV-filter coating. As we all know from getting sunburns, UV rays BURN flesh, be it the skin of a leaf, or the skin of our body. So keep this in mind when you're talking about unfiltered/direct light "indoors" versus direct/unfiltered light "outdoors". Just because your plant can handle several hours of indoor light directly doesn't mean it can take it oudoor.
Granted, some of us live in old homes with single-pane glass windows or lead windows with no UV coating... something else to think about.
Just my process.... your mileage may vary.
You will get to know "leaf scorch" very well if you put your plants outdoors too soon, or for too long of a period in direct sunlight. It will take a couple of days to show the effect - you can screw up one time, one day, for a couple hours too long, and it won't show up for a week. So...be careful.
Leaf scorch won't kill them, but the leaves will turn bleach white and shrivel. New leaves will grow out to replace them, but ... it's just another hit your plant can take in development.