Thanks for sharing the form with me.
I've updated the form and added back the expression to show time submitted.
Just in case, the way to get info back - is to add expression into the column: =LOCALTIME(ROWCREATEDATE()) but note that currently I've locked the column (via Table->Lock) so if you would need to change the expression you need to unlock the column first.
Do you remember what operations lead to lost of time info? (we try to prevent inadvertent edit of the time column by locking it, so I am trying to figure out root cause of the problem, and if we can do more to prevent such errors in the future).