In regards to the 1:
A. In the data pane, right click the User ID field (or the field you would like to use to answer the question "Does this field value have 2 timestamps?") I am just assuming it's User ID. Select Create > Set.
B. In the Set menu, navigate to the Condition Tab and enter a formula similar to the following:
count([Date/Time complete]) > 1
C. Click Ok. This puts User ID's in the set if they have more than 1 timestamp. We can now use this set in the view or use it to filter the view. Below is some additional information on computed sets:
As for number 2, I may need a bit more information. We should be able to drag these fields into the view and then filter using the set we created above.
If this doesn't help, are you able to share a workbook?