I’m still not sure when to use ‘depuis des heures’ as oppose to ‘pendant des heures’. Does 'pendant des heurs convey more flexibility in terms of when an activity began and ended ?
You sleep for hours every day.Tu dors pendant des heures chaque jour.(??)
It is not about ‘flexibility’, or at least I would not put it like that. Consider the following examples:
Thanks DPRK. According to the link you posted it would seem that since pendant has “no relation to the present” then ‘pendant des heures’ would be correct in my example :
You sleep for hours every day.Tu dors pendant des heures chaque jour.
Exactly. “Depuis” is for a duration that goes to the present time and “Pendant” for a duration that is finished, or for is recurrent.
“Tu dors pendant des heures” implies you sleeps for hours regularly.
“Tu dors depuis des heures” implies you just wake up and had been sleeping since hours.