To answer a few questions:
My background is having ridden a short commute to work for a number of years (6 miles round trip) before I retired 10 years ago then taking up riding again a year ago last spring. The terrain is relatively flat although there are a few hills to make it interesting. In figuring my time there is no warm up or time spent winding down after. I just get on the bike and go. There are a few places where I am forced to slow down because of bad conditions in the road and a few intersections that deserve a little respect but only one traffic light and two or three stop signs.

As to intervals I am not disciplined enough to follow any regime but I do find that if somebody sails by I can't help going all out to try to catch up.