I can't say for certain, but I've mixed meth with a few things and never noticed any impact to duration of those other substances. Substances like LSD, mushrooms, heroin and fentanyl to be exact. I noticed that the LSD high isn't shit when using meth, like it blocks it from its full potency somehow. Same duration though. Mushrooms I microdosed and everything seemed as normal as can be while mixing shrooms and meth. H and Fentanyl have both put me from being as high as a kite on some good meth to nodded out and waking up sobering up hours later.