I would like to block the possibility to enter time on the activity. Is it possible?

Just don't define assignments to this activity.

or is it possible to block the entry time on a type of project and not others ?

No.On a projet, yes (depending on rights) but not on type of project.

without define assignement of resource on activity, when the ticket is just create and without real work on it, activity doesn't appears. But when the resource enter real time on ticket, activity appears and asignement is automatically create, so the resource can enter real work on activity.

any idea ? why the assignement is automatically created on activity when real works are enter on ticket?

Explanation about this behavior is in the manual.

See Ticket topic: ../docs/user/html_en/Ticket.html

I read the manual about it and I understand the functioning. I do not understand why resources can enter time on the activity of the attached ticket. In the management of rights, these resources have just read access to activities. In fact I would like the resources, based on their right to access, can only enter the time on the tickets.

You're right.
This possibility was first given in the idea to ease work entry, because in most cases, "delays between tickets" is not recorded on the tickets, but should be entered somewhere...

We'll have a look to give more fluent input.
Request recorded as Ticket #2360