With timechart/stats you can "split-by". In this case i think you want to split by "server".
index="monitoring" Servers | timechart span=10m sum(UnusedCountBelow100) as DB<100sec sum(TAUnusedCountAbove100) as DB<500sec by server
Update:
Reading more closely it looks like you don't want to split, and that timechart might not be working as expected. You may want to submit a ticket on this, but you could also try stats followed by timechart:
index="monitoring" Servers | stats sum(UnusedCountBelow100) as DB<100sec, sum(TAUnusedCountAbove100) as DB<500sec by _time | timechart span=10m sum(DB<100sec) as DB<100sec, sum(DB<500sec) as DB<500sec
Also, in your sample above, if that is a single event I would recommend turning off line merging such that each line is a single event. "SHOULD_LINEMERGE = false" in props.conf
... View more