I suggest that you go to Google Scholar and input your search terms 'longitudinal repeated measures marketing' or some such variant. Some papers of interest will come up. Check their methodology sections to see if there is one which you can replicate for your study. I have attached a sample paper here, but your research question may not exactly match of course. Also, you can link in with the research authors on research gate and see if you can find/ask for a more exact match. A link to a recent monograph on longitudinal research is also provided below.

https://books.google.ie/books?id=5bD4LuAFq0oC&printsec=frontcover&dq=longitudinal+method&hl=en&sa=X&redir_esc=y#v=onepage&q=longitudinal%20method&f=false

Thank you so much Michelle B. Cowley . It really helped. 

Dear Jaha,

When we conduct a longitudinal research there are, as far as I know, no standard guides to follow, both regarding the number of repeated measures as well as the timing (gaps between each repeated measure). What I have for sure is that only longitudinal research leads us to assess intraindividual change, which is quintessential to developmental psychology and developmental studies, Unfortunately, developmentalists often appeal to cross-sectional studies, As you certainly know, cross-sectional sudies are unable to assess intra-individual change and thus these studies are not developmental studies at all. Of course, a Google search can be of much help for you.  But the questions you raise, number of repeated measure and the time interval between them depends on a myriad of factors, such as the topic you are addressing, the goal of your longitudinal study, your participants' age, and so forth. I am a develomental psychologist. I often used three repeated measures. The gap between two repeated measures was generally about 2-years. Note, however, that my longitudinal world ranged from 4-year- olds to 10 year- olds,

Let me say that, as in any research, it  is more important  that you are able to raise, say, "irritating" questions or doubts -- that is, questions whose answer leads us to advance knowledge and a better knowledge of the unknown  -- than to be concerned with the problems you raise. Of course, in any research, there should be conceptual clarity.

Best regards,

Orlando

Thank you and very well said Orlando M Lourenço. And with every response to my post, I am getting more useful points to move forward with my project. 

Here are some resources for longitudinal design

http://www.bristol.ac.uk/cmm/software/mlwin/mlwin-resources.html#datadesign

More specifically software for design:

Raudenbush, S. W., et al. (2011). Optimal Design Software for Multi-level and Longitudinal Research (Version 3.01) [Software]. Available from www.wtgrantfoundation.org.

Documentation:

Spybrook, J., et al. (2011). Optimal Design for Longitudinal and Multilevel Research: Documentation for the Optimal Design Software Version 3.0. Available from www.wtgrantfoundation.org.

These can be freely accessed at

http://sitemaker.umich.edu/group-based/optimal_design_software

Thank you so much Kelvyn Jones. I am obliged.