Rest time for testing lipo cells
The statement that "some bad cells may charge and discharge to the nominal capacity if they are charged immediately, but do not hold up after time" it is very slightly correct and it refers to the fact that the internal resistance varies slightly with different cells and after a VERY long time an imbalance will appear.

Just as mkeith said, all you need to do is measure the OCV (open circuit voltage) and match cells which are very close one to another and put them in series. Then put the closely matched series packs in parallel.