Enter day tasks in Calendar without times I feel constrained when I need to enter start and end time for a task because I know it can take another amount of time than entered.

Can I somehow just make a list of tasks for a day, one after another?
I saw all-day tasks, but I don't think these are what I need.

As an alternative, what tasks list could you recommend please?
In Calendar, you can use the all-day events, that are shown one after the other.
Otherwise, you can choose among multiple apps. For free:

There is the default app Reminders, that allows you to create lists of events that you can check once completed.
One app I really like is Wunderlist. It has a good layout. It does more or less the same as Reminders, but it has much more functionalities. Obviously, you can sync with other devices.
You can also use Trello, which is an app for mobile phones and you can use on your Mac through the website. I consider that Trello is very complete but a little trickier.

Of course there are much more apps. It depends to your personal taste. De gustibus...