Translation:Usually, I run in the afternoon.
Swedish allows for a quite free word order and things can be moved to the front for emphasis to a higher extent than in English. If you’d start with the subject, it would be: ”Jag springer vanligtvis på eftermiddagen”, then the adverb comes after the verb. But if you wanna stress the ”usually” part, you can move it to the front as in this example. Swedish also has a ”verb second” rule so if you move it to the front you have to make sure the verb (springer) comes after it.
so i [time of day] is used for phrases that point to certain times (like i kväll, i natt, and i morgon meaning this evening, tonight, tomorrow). But when you want to say during/at/in [time of day] you use på and the infinitve? So it's basically like the difference between saying tonight and in the night/at night in English?