RC/PE2>iM: 30s each side or total?

Regarding RC/PE2>iM Bent Sideways Lat Stretch (or any exercise with a one-sided stretch), how do we alternate sides? This particular exercise is written as 30 seconds per set, but does that mean:

• 1 set = 30 second one side, 30 second other side (i.e. 60 seconds total stretching per set)
• 1 set = 15 seconds one side, 15 seconds other side (i.e. 30 seconds total stretching per set)
• 1 set = 30 seconds one side, but alternate sides every set

I've been doing the third one with an additional set for the less-worked side on odd set counts (so 3 sets looks like: rows/left, rows/right, rows/left/right).

 

30 seconds each side after each set.

Wow, really?? For some reason I didn't think this was the case. I cheated myself out of some extra rest! So for RC PE3 iM, the Bent Twisting Lat Static, it's 30 seconds on each side as well for a minute total of stretch?