If we go by your list you have to compare beta 5 to beta 6, because beta 1 is most likely beta 2 internally due to WWDC being roughly 3 weeks late compared to the years before.Time passed between beta 4 and beta 5:
iOS 5: 15 days
iOS 6: N/A
iOS 7: 8 days
iOS 8: 14 days
iOS 9: 16 days
iOS 10: 8 days
iOS 11: 14 days
iOS 12: 13 days
iOS 13: 12 days
Not impossible it comes out this week, but likely next week