Backup window for different vault stores in EV.

Dear's,

I have 3 EV 10.0.3 servers with indexing configured on all three servers.Exchange is 2013.

We have single EV site with 1 vault store group and 6 vault stores, sharing level is configured as within vault store group.

We have users working in different time zone so need to have different archiving window for all the three server which is possible using archiving task but i need to create backup script so that only 2 vault stores are in backup mode at a time.
I need to know the best way how can I keep few vault stores in backup mode without affecting the users in the remaining 4 vault stores and also, when should I have indexing in backup mode.