The RA begins at the start of the day (0130) and the RB begins at +12 from the start of the day
and they are by definition 12 hours. the other paragraph refers to the END of the R period so i think it means 0530 (0130 + 4) or 1730 (1330 + 4) to be shceduled for crew rest.



2. Reserve Periods (RP)
a. Reserve periods may take any of the following forms:
i. Reserve Period A (RP-A) is a 12 hour period of time
beginning at the start of the day.
iii. Reserve Period B (RP-B) is a 12 hour period of time
beginning 12 hours after the start of the day.