I have seen some people using different ways to track different parameters like sleep, fast etc. I think the important value of this project is not how the users are entering the data but how you are going to show/visualise the data. You can have a better chance of convincing the users if they can see different visualisation of their activities.

In one sentence, you are not only helping the users enter the data in an easy way but also helping them get the hidden insights of their activities by showing them different visualisations of that data.