I've been doing a blend of shibari and tantra for years.

I've always considered it to be a "slow burn" kind of loving as opposed to the "flash" of BDSM.

The blend to me is a way of keeping pleasure alive for a very long time. While I have not personally hit the six hour mark, I have made it well beyond three. I know my dorei loves those sessions where the shibari is in a kind of free flow zen space while we're both at that plateau before the final orgasm.

Just to clarify... I'm calling BDSM sex more of a flash, because in the way I've done it over the years, it seems more like I'm ripping orgasms from my girl, rather than letting her simmer for a good long time.

Of course, you have to know your ropes, and both your bodies well to do it.