Very interesting thread. the man to ask but now is dead would be Terrrace McKenna, he wrote the book about all of this. I have used LSD, Shrooms, DMT, ayahuasca which by itself does nothing it has to be combined with a plant that has DMT in it to work and by fardoug wrote:"DMT, The Spirit Molecule" by Strassman may be of interest to you.
DMT is present in our brains and many, many natural sources, some of which possess high content and used to extract the compound from in a fairly simple process. The "how to" is available on the Internet as well as the plants to extract it from which are not illegal (but the DMT is of course).
The effects of DMT, mushrooms, LSD, are similar, conciousness expanding, and safe providing the appropriate preps. These medicines, compounds, sacraments or whatever we choose to call them can and do provide life experiences that are usually association with epiphanies, mystical, religious, life changing, etc.
The time duration you describe would be from smoking DMT extract. Ingesting it lasts much longer as it is combined with other natural compounds such as in ayahuasca, the brew used safely by South Americans in religious ceremonies for centuries.
It's a fascinating topic but the experiences are even more so.
ayahuasca journey is not something you can say was joyful. DMT can easly be extracted from red canary grass that grows wild. I do agree with the other posters here in some areas and others not. When your speaking about this class of drugs the experience really depends on who is guiding you through. If you have a spiritual guide it can be amazing, if you just do it to see what happens you really dilute what your experience will be.
Plus there is always a danger some people brains are not wired at all for this and they will have a bad trip. I never had a bad trip and I do not use drugs now but they can open a door of perception for you but at the end of the day I doubt they will really help your progress much. The other main problem is and has been already mentioned these drugs do overload your senses , they enchance the sense so much that it is very hard to find your center so anything you think you might gain is easly lost in a sec or so.