You made the claim, that Kakashi can use it for no longer than 5 minutes. So I would like a proof that proves your claim.
How long could Madara use his PS?
No matter how long, Kakashi can use it longer, thanks to Rikudo's Chakra which puts him above Madara.
EMS user don't seem to have their Chakra drained by the usage of MS techniques. A MS user feels pain in every cell using a normal Susanoo and collapses after combining it with Amaterasu, but an EMS user spamms techniques and uses a Susanoo of titanic proportions and keeping a straight face.