The challenge with claims involving Ruling 96-8p, where the issue is the claimant's ability to maintain a full-time schedule, is that Social Security's forms – such as the Medical Source Statement of Ability to do Work-Related Activities (Physical) – have no spot for a doctor's opinion regarding a patient's ability to maintain a regular work schedule.
As a disability lawyer, you need to get the doctor's opinion on this issue. It's really important.
Do you whatever you have to do. Ask the doctor for a narrative. Type in the question on the form you send to the doctor. But somehow, get the doctor's medical opinion about whether or not the claimant can sustain a full-time work week (and if not, why not).