pi.explain  the technology type . Period may vary from one to other technology. secondly what is status of population under study , it will be a vital factor while deciding time interval, . 

 Technology adoption is in context of financial services automation.

Dear Anoop,

Longitudinal studies are very often panel studies. We are measuring the change over time with the same panel.  For example you collect data on selected industry under criteria designed  by you according to your research question. the time gap also depend on the changes that you anticipated. If it is financial service innovation you can compare outcome before the adoption and after adoption. 

Most of the books on experimental designs discuss about longitudinal studies even population studios. There is no term as ideal gap. generally difference should be significant enough to be measured. 

Upananda

Dear Sir,

Thanks  a lot. I got your point.

Regrads

Dear Anoop,

Thanks for your positive response.

Upananda

this gap may be atleast SIX months.

Thanks Ijaz Sir,

I will keep this is mind while doing my data collection.. 

Regards

ideal gap means qualitative sampling, it requires more than six months to study the comparative nature before adoption and after adoption. take at least two qualitative parameters for good results.