When something happens in a month it's "im", but for a time of the day it's "am". Is there a rule or do we just need to remmember the preposition for each type of time?
You just need to remember the prepositions used. Prepositions often don't translate exactly between languages, so memorization is best in general, too.
In one of the earlier sentences -"Sie isst jeden Morgen Müsli" the "time" is in the middle of the sentence, while the verb is last.
But in this one it is the opposite, is there any rule for this?