Hi Mahesh,
Custom Traffic variables are a data dimension and do not function and are not available as metrics in Adobe Analytics. Time is also not a metric, but a standard data dimension by hour, day, week, month, etc. However custom traffic variables allow for correlations against other traffic variables. I would recommend exploring this option, but you likely need to also allocate a time stamp custom traffic prop as well.
Help Link on correlations below:
http://helpx.adobe.com/analytics/kb/comparing-correlations-subrelations.html
Best,
Brian