The best times are just after sunrise and about an hour before sunset.
In Gothenburg, the times vary with the seasons. In summer, sunrise is around 4:00 AM and sunset around 11:00 PM — so you can fish very early in the morning and late in the evening. In autumn, sunrise is around 8:00 AM and sunset around 6:00 PM, which means you can sleep longer and still have time to fish during good hours.