Hi,
This can be accomplished by having a column for each of the checkboxes, then when you have both checkboxes in the one datacard, you have the separate (completed) column's DataCard show the value of that textbox, then hide that additional datacard - do the same for the other additional cards.
Create you have 'arrival date/time' column for Assign,
Create column for 'arrival date/time' for the completed value.
Create new data card below that row, with the value of the item being that completed checkbox in the above datacard.
set visibility of the new data card to false.
Now when you tick that checkbox for completed, that value in that hidden column is updated and then submitted with the form
Repeat for the other checkboxes and columns.
Could you give that a try and let us know if that works?
If you have already solved this question yourself please do let us know how you resolved it,
Many Thanks,
ManCat