Sadly, I've never found any positive research that there's any way to do it safely. When I was younger I found schedules like the Uberman[0] and was amazed by the claim: only 2 hours of sleep a day required, as long as you stuck to a pretty rigid schedule and were disciplined about napping on time. I never had the scheduling freedom available to actually give it a go, and accounts of others trying it seemed to indicate that it was actually pretty awful to keep up.
This article seems promising, but it's a relatively short experiment. Would be interesting to see what happened after a year of 4 hour sleep. Based on the author's description, sounds like their body was trying to force them asleep at every turn and they had to fight through it. That would be hard to maintain long-term.
I truly wish one day we can isolate and synthesize whatever magical thing happens during sleep and recover some useful time. This seems much more practical than life-expectancy extension to me. As long as, of course, employers don't take it upon themselves to increase the workday as well. I'd rather sleep than work.