You can either install Failover/Load balancer or install a replication partner and set the replication schedule of business hours.
Do not replicate Content and let the other SEPM down its content.Thus less bandwidth will be consume even between SEPMs.
Now Create Management server List with Priority 1 as New SEPM and Priority2 as Old SEPM and assign it to the groups you want to manage with new SEPM.
You can either create 1 more Management server list with opposite settings so that if Main SEPM fails clients can go to New SEPM or else leave it as it is.