Hello :) There are many different kinds of orchids and each kind is grown a bit differently so the answer would vary. What kind of an orchid do you have? If you're not sure what it is you can google "phalaenopsis" which is one of the most popular orchids and easily available locally. The American Orchid Society also has culture sheets with pictures of other kinds of orchids which might help you identify it AOS Culture Sheets Please post again and say what kind it is so someone can help you. You can also include a picture of your orchid in your post which would be helpful. How to include images in a post

With cuttings, anything can go wrong, but I would focus on hydration/heat, first, then the mix you're using second. On a 95F day, plants can dry out very fast. A small cutting can't pull water fast enough from the soil to keep up. You also have to be careful about transplanting them into a mix that's too hot. I normally pot up in pro-mix, which has zero fertilizer, and use a very weak solution of Miracle Gro to feed them for a month or two. With a small cutting, too much fertilizer (organic included) can cook them.

It seems like they could be dying from the bottom up! I've had that happen with many of my cuttings but they only die up to the soil level. If they are dying from the bottom, you could cut them off and re-plant the tops. But it's a tough call because that is risky, and it may not be what is actually happening. Can you post pictures? I just asked someone in another thread how many hours a day you can run a lamp on roses, but without an answer yet I would STRONGLY suggest you put them on a timer to be safe. I do know the vast majority of plants require a daily dark period in order to grow properly. Try 16 hours a day of light, giving them 8 hours of darkness which mimics the longest days of summer. I've seen growers of some types of plants push that even higher - up to 18 or 20 hours - but they always allow some darkness. Maybe lack of a dark period is what's preventing the cuttings from setting properly. Also, make sure the lamp you are using is sold as a light for plants, or is a full-spectrum light as similar as possible to sunlight, rather than an incandescent lamp which is not only hot, but usually tilted towards reddish/yellowish wavelengths which do not give plants what they need. Different wavelengths initiate different processes in a plant and help regulate growth.

I can only offer advice for my own personal experiences in a very hot and dry area of northern CA. I put new cuttings in an area that gets only dappled sun (or even more shade) from about noon on if the bag is coming off. Sometimes it helps to just open the bag too so it gets used to it like you were saying, but if the bag is already off what I would do is make sure to water it daily, put it in an area that gets afternoon shade, and not a lot of reflected heat. Mulch seems to help too by keeping it cool and keeping some moisture in. The best advice may be totally different for your area though! Hopefully another with more expertise will offer advice too.