Could solitary confinement be an appropriate long term sentence for convicted murderers if the standard was modified?

Currently (at least to my knowledge) the standard for solitary confinement is a 22–24 hour lockdown. I personally feel that even 22 hours is too long to keep a person in isolation.

So I am wondering, if the standard was modified to a 20 hour lockdown. Also allowing inmates with solitary sentences 4 hours of non-isolation a day distributed at different intervals throughout the day.

In your opinion would this suffice to reduce the likelihood of mental distress for potential inmates sentenced to a possible 20 years plus of solitary confinement for the crime of murder?