Ochtend is specifically the morning i.e. s'ochtends eet ik ontbijt (I have breakfast in the morning) , morgen on the otherhand usually means tomorrow i.e. Morgen ga ik naar huis (tomorrow I am going home) But it can be used as morning though to me it sounds a bit wrong. in de morgen eet ik ontbijt (I have breakfast in the morning)
Since " (de)s morgens" is self-evidently an old genitive of time within which, a translation as "during the morning" or "in the course of the morning" really ought to be allowed. It is interesting, by the way, that the genitive of time within which was able to maintain itself in Dutch. In Low German, which has otherwise completely lost the genitive, this particular type of genitive is still around; and even in colloquial High German, where various uses of the genitive are currently under threat, the genitives of time have no competition.
the problem with "during the morning" or "in the course of the morning" is that it implies that you take the entire morning to get dressed, whereas the sentence's meaning is that you get dressed in the morning without any time frame as to how long it will take you to get dressed.