I had a look at the app, there, labels seem to be stagnant labeling, there seems to be dynamic labeling for AGOL as an idea in Geonet
Dynamic Map Services in ArcGIS Online
Until then the pop-ups and the legend you have created dose well, the user can click on the polygon and the pop-up will tell them the day they need their bins out.
FYI, when creating or editing the web app, at the bottom left-hand side, you can see the preview of your app before you publish it.