Hello gujintao7890,   The iDRAC updates you could do all at one time. Only the DRAC reboots, not the host, when the DRAC firmware is updated. For the BIOS, that would require a host reboot.   If you do one update job including all servers then you can select Stage for next server reboot, then reboot the server when you want it to update. If you do one update job per server you can use Schedule Later and specify a date and time   Bulk system update - cannot schedule individual date/time to update. Individual system update - can schedule date/time to update.  
Good morning. I would like to update the firmware on the R630 and R730xd servers. There are more than 150 of them in total, and I would like to perform the update on each of them separately, and separate these updates with an hour break. Is there a solution to automate this task from within Dell OpenManage? Regards
Performing iDRAC and BIOS update on multiple servers one by one with Dell 
OpenManage