How to create the longest time of concentration path in a Watershed?

[AndrewMartin8]

So I just finished creating the longest possible flow path in a watershed. Now I want to create a path for the longest time of concentration path in a watershed. What is the best way to approach this?

I used flow direction, flow length and the maxcell to create the costpath and then I converted it to a polyline. What other information do I need for the time of concentration path?