UPS actual power supplied is 60% of its VA rating so 1000KVA ups provides (1000*0.60)=600W of power. Backup time depends on actual system power load,battery size & its age(older the battery lesser will be its charge storing capacity). At full load of 600W(which you will not reach unless seriously overclocking a hexa core processor & a 1080/equivalent graphics card) it gives ~3.8min of backup.
- APC USA