It is nessesery to have 24 to 48 hours darkness before harvest?? ?

No it is not necessary and personally I would strongly advise against doing so. There is no concrete evidence that it is actually effective, or even beneficial, in all cases, with all plants and at all times. To me it seems a high stress technique, and the last thing I would ever do is to stress my plants right before harvest and after weeks/months of careful attention. Through experiments conducted over the last 25+ years, I believe my preferred harvest time is approximately 1-2 hours after lights come on and after a normal night of normal length. This seems to produce flowers with the tastiest cannabinoids and the most aromatic terpenes. This has involved harvesting plants at nearly every hour of the day and at random times during the night, including 3am, which produced the blandest buds. Hope this helps, Organoman.

The change in thc is minimal at best with a dark period. I use to get my weed tested all the time and I took a normal cropped plants bud in to be tested and one with 24 hour dark period and one with a 48 hour dark period. The only change I seen was in the 48 hour dark period, and that change was the buds shrunk a little in the darkness. The first plant I took with no dark came in at 22% thc the second, the 24 hour dark came in at 21 thc and the 48 hour darkness came in a touch higher at 23 thc.They were all clones of the same pheno. I have taken strains of the same phenols in many times to have the same results. Even clones come in a little different any time I had my bud tested without any dark period. So to lose a little weight with a 48 hour dark period is not worth it to me. For a 1% difference, I could never tell when I smoked it. So no dark periods before harvest for me. Cheers

https://imgur.com/qSgXTJp <= darkness before harvest baked with lab results darkness before harvest slighty increase potency, but reduce terpene

Also a bathroom should work just fine as long as you can maintain the proper temps and humidity for drying.

Apparently it increases trichome production so probably worth having a go even if it is bro-science.