Sorry for the delay. I wanted to make sure I reviewed the OPNIAVINST.
The regulation that controls this is OPNAV INSTRUCTION 6110.1J. This is the regulation that controls the Navy’s Physical Readiness Program. It provides guidance to commander's on what steps to take for Sailors who are overweight, or failing the PRT.
The current policy is Sailors in this program should participate in
(a) Two hours and 30 minutes (150 minutes) per week, i.e., 50 minutes three times per week or 75 minutes two times per week; plus
(b) Perform strength training exercises at least twice per week to work all major muscle groups.
So they can require 3 50 min sessions. There is no limitation on the same day.
I agree with you, it does not make much sense to have 2 on the same day. To get the most out of the exercise there should be time for the body to recover.
But the rule does not make limitations on how long or how often the exercises can be required. IT leaves that to the commander.
So the short answer is yes, you can be required to attend 2x in one day.
I would consider requesting mast to discuss with the commander...it may be they can modify your work schedule to allow you maximum benefit from the exercises.