I'd like to create app with 3 months exercise plan. There will be around 30 exercises to do every day but time is growing. What is best way to keep values of minutes in every exercises and which one exercises you should do today. Im using Firebase in this project but im not sure about optimalization because there will be much datas just from exercises. Every exercises has photo how to do this, time and description and I need to store the length of the exercise for each day so I do not know if this is a good solution.
You could use a relational Database like MySQL, PostgreSQL, MariaDB to store the data server-side.
If you want to persist the data on the Android-side of things use SQLite https://developer.android.com/training/data-storage/sqlite
If you application doesn't require online connectivity all the time, a nice idea would be to be able to sync the server DB with the android DB for offline usage.