I made my weekly task much faster. Should I tell my manager before I know what fills the time?

The files merged in twelve minutes. Last week, the same job had taken me most of an afternoon.

I prepare an internal list of exhibition bookings. I’ve built a spreadsheet routine that combines the exported lists and flags duplicate entries. I checked this week’s result against my usual method and found the same bookings. I haven’t tried it on every variation of the files yet.

I’m pleased with it. I’m also nervous. My manager thinks the task occupies a substantial part of my week, and I don’t know what work would replace it. The rest of the team is busy, but none of their tasks is an obvious fit.

I don’t want to keep pretending the merge takes three hours. I also don’t want one promising trial to be treated as proof that the whole job now needs less time.

How would you show the improvement honestly and discuss what happens next?