"He is there for at least one day."
Translation:Il est là pour au moins une journée.
I found this really useful! http://french.about.com/od/vocabulary/a/an-annee-jour-journee-matin-matinee-soir-soiree.htm Hope it helps :)
why does "c'est" work for he is or she is sometimes but not in this case? I know c'est la (accent over the a in la) means it is there, but I thought "c'est" could be used interchangeably with "Il est" or "elle est"... Can someone explain to me when it is and is not appropriate to use "c'est" for "il est" or "elle est," as I have seen it done on this site? Thanks in advance!!
My bad, did not read properly what your issue was.
"Pour un jour" tends to announce a plan, an intention.
- il est/sera/était là pour un jour = he is/will be/was there for a day
"Pendant un jour" relates to the actual duration.
- il reste/restera/est resté pendant un jour : he stays/will stay/stayed for a day.
However, as soon as you use "for + duration + present perfect", the French changes in tense and preposition:
- he has been there for one day = il est là depuis un jour