I used Google Calender for mine, and synced it across my phone which allows popup notifications as well.
You can start by crossing out portions of your day where you definitely won't have any time for study (e.g. school, sleep, piano, exercise, travelling etc).
Next, identify parts of your day where you know you have time for study, for example I usually have to wake up early in the morning anyway so I have about an hour to make notes or do hw, but majority of the time it's after school.
Use 40min blocks when you're studying, meaning you study for 40mins and take a 5min break, and continue on (adjust it for personal preference).
You shouldn't divide time equally between all your subjects, rather make notes or do assignments as you see fit (this leaves for a lot of flexibility). It's purely up to your judgement on the subject of how much time to spend on your subjects, think how much the workload is for particular subjects.
The one thing that is heavily advised is consistency. Making the timetable is the easy part, but actually sticking to it throughout the term is harder. I created mine with 4 hours of study each day, but after a week stopped following it.
Goodluck! Try making one today, and trial it on the remaining week we have left before school starts
