The time planning is based on day not hour or what is really needed

Project Management is rarely used to plan "1 hour" tasks.
This is mostly some production management, not project management.
When managing project, planning tasks 1 hour long will take more time to plane the project than to execute the tasks...
So duration is always calculated in days, never un hours.
But you can plan several tasks of 1 hour on the same day (as long as the resource has the available capacity)

NB : you your issue is due to dependencies, have a look at "non strict" dependency mode, in global parameters.