What is the difference between temporal "en" and "dum"?

Question

It seems that I slept during the holiday can be translated into two ways:

Mi dormis en la festotago.

Mi dormis dum la festotago.

Do they both mean the same?

Answer 1

Your two sentences mean different things.

Dum implies duration. En suggests that something happened within the period.

• Mi dormis en la festotago.

At some point you slept.

• Mi dormis dum la festotago.

You spent your festival day sleeping.

Answer 2

PMEG has a paragraph about this. http://bertilow.com/pmeg/gramatiko/rolmontriloj/rolvortetoj/lokaj_rolvortetoj/en.html#i-sb8

Dum shows a duration (over which the action took place). En can show one of two things

• a point in time
• the time needed to complete an action, basically the point in time when the action will be finished.

You can also have temporal tra and por.

Mi dormis tra la festotago - almost the same as with dum, but with emphasis on sleeping through the whole period.

Mi ripozis por unu tago - I took a break which lasted one day.