You could try something like LiquidTime. I think it's still in beta (since 2016), but its super simple and has a really nice UI. It sizes tasks according to the amount of time needed for them. Otherwise good old Google Calendar works pretty damn well for showing tasks within a short time period & resizing tasks according to length..
This website lets you decide how many hours you want to work/plan for a day and then lets you add categories with how many hours you want to spend on during the week and amount of time per session. Then you can allocate the hours throughout the week.
A downside to this website though is that you can't schedule exactly what time you plan to work on something. It could be useful for planning though, and you could adjust the times later based on what you actually did and then reallocate them.
Another alternative is google calendar. You could use liquid time to plan how much time you want to spend on something per day, and then actually schedule a specific time on google calendar.