Hi there
It sort of depends on how early in May, I would try to avoid the first weekend since it may be pretty crowded then (long weekend here in Sweden). Fridays and Sundays are better than Saturdays...
Thanks so much for replying and with all of that information. I will hold off until the opening hours are released. Cannot wait to ride Helix (and Balder!) and spend a day or two in Gothenburg!