Hi there, since the April update, I've noticed my issue has been fixed. I suspect this issue only affected the Exynos variant of the S7.
Also when you say instantly, what exactly do you mean by that? If you're getting "instant" wake-ups ***without*** the Always-on Display (AOD) enabled, then I really want your phone! I generally get near "instant" wake ups with the AOD enabled, but a 0.5-1 second total lag without it enabled. Before the fix, the total lag was about 1-1.5 seconds (AOD disabled).
This issue is discussed in great detail in this forum/thread, and I made a post there too (check out the YouTube video at the top of that page):
Galaxy S7 slow to wake - Pg. 17 | Samsung Galaxy S7