Please let me know if these references/sites are helpful to you:

1.  Patient Recruitment and Retention - NC TraCS Institute

https://tracs.unc.edu/docs/research/Recruitment_and_Retention_eBook.pdf

Recruiting and enrolling patients for clinical trials can often be a long and ... Patient Recruitment and Retention | Forte Research Systems, Inc. ..... may need to consider extending the recruitment period, if possible, .... Is your waiting room.

2.  Clinical Trials Patient Recruiting and Retention: Tips for ... - Mosio

http://www.mosio.com/rxajdoeajRsd0320/Mosio_Patient_RR_Ebook_2014.pdf

Tips by inVentiv Clinical Trial Recruitment Solutions . ... tips to add to your patient recruiting and retention toolbox in the 68 we provide. As the landscape of media, ..... Don't wait until you have a problem to execute your plan; be ..... Cycle 2: Cycle 3: Cycle 4: Sign Informed Consent. Stop Drug 1 prior to hos- pital admis- sion.

3.  Clinical research - Association of Clinical Research Organizations

https://www.acrohealth.org/wp-content/uploads/2014/10/acro-white-paper-tah10.pdfCase 2 - Innovation in Trial Recruitment Speeds the Clinical Trial Process .... invaluable period of time for patients in need of treatments. .....

Dennis

Dennis Mazur

If someone is depressed and untreated, you cannot wait  more than a few days without providing effective treatment. 

If the intervention is a group exercise program and the depressed participants are in medical treatment, you can provide everybody with individual exercises which the control group can continue when the intervention group moves on into the group.

Both answers were very helpful. Thank you Drs Seeman and Mazur. I was thinking of having antidepressant use start with recruitment and continue for those randomized to the control group. Group exercise classes would be tough to manage during recruitment. Maybe unsupervised individual exercises on their own would be best. 

Consider also the fact that individual instruction concerning excercise during waiting for group sessions to begin is truly individual therapy (standard standard error formulae hold), whereas group therapy in principle is subject to group mechanisms, potentially violating the usual assumption that participants' responses are independent (a clustered analysis may give the right SEs that standard formulae fail to provide).

It is a complication (a) that gradually recruited patients will have different waiting times, hence unequal response to the individual-period training, (2) and that this response must somehow be amalgamated with the same patient's response during group period. In the end a sophisticated statistical model - and professional assistance - may be needed.

Dear Spencer:

 May I say that your question leaves out details that would enable one to provide a cogent response to you.  However, let’s assume that all subjects are already undergoing treatment with standard of care for depression and will remain on such treatment(s) during the study.  If that is the case, then it will depend on what it is you are doing during the intervening period between recruitment and randomization.  Another consideration or question is when you consent subjects and what you tell them this period is to be used for.  There are a number of other points of consideration that come to mind, but in deference to pithiness in this forum I shall stop with the ones I’ve highlighted above.  Good luck

 Cheers,

Chuke