That would be correct if you where using the verb "trovarsi", which means "to be" referred to a place where you are, and that doesn't make sense here. You can also recognize that the verb is not "trovarsi" because it's intransitive, and here "tempo" is a direct object, so you need a transitive verb.
As a result, you have to assume that the verb used in the sentence is the impersonal form of the verb "trovare" (which is transitive).
Actually "si" is not being used as a reflexive but rather a form known as the "impersonal si".
It puts a sentence into passive voice and is equivalent to an English expression using "one" as the subject. I don't think Duolingo has covered this before. But, one never knows.
Hopefully the links will help.
Sì = yes. Si = one's self. It's the subtle differences you have to watch out for!