I wish I could select "between 2.5 and 6 minutes". That search can translate to 2 queries to YouTube (<4 and 4-20), then the results can be combined and pruned to keep only those between 2.5 and 6. To get enough videos if there aren't enough after pruning, we could access the 2nd, 3rd and so on pages from the results. But I doubt YouTube will like 6 searches in a row.