Dashboards - create a queries for transactions happened in the last 10 minutes

Hey there!
I’d like to create a dashboard (using Big Number chart) which will show a count() of transaction which happended in the last 10 minutes. In order to do that I add age:-10m tag to the query but it returns no results - same thing happens even if I change to age:-24h - but without that tag I get many results (and their age is surely within specified window). What am I missing?