You have to figure out which sections need how much or how little. Then take the base time and add /subtract each section. It helps to make yourself a grid pattern and check off sections as you work. Hopefully you don't have a large number of these to track.

for example the over all time for an exposure is 22 sec. you want to dodge out 4 secs in two areas, so the last 8 sec of the 22 would be divided into 2 actions, each getting a 4 sec dodge. Then which areas need a burn and do them one at a time.

Hope this makes sense.