Spent a lot more time in Z4 than I expected. Though, I just compared to the two rides last week on this route, and they were very similar. Hills = higher HR. The recent heat isn't helping.
Sunday was fairly similar on the mountain bike: Z2 = 22 minutes; Z3 = 35 minutes; Z4 = 30 minutes. Apparently I haven't spent much time in Z5 lately. No worries, though - my last race I spent over 15 minutes there!