How to define granularity for daily based time series?

I am creating an app that should contain aprox 100 daily data parameters. I am benchmarking the normal collection vs time-series approach. The app is mainly for analytics.

My concern is about granularity, the right granularity does not exist in this case “days”, Which is the impact selecting the closest one “hours”.

In any case the app would require filling nor densify options.