mmin not working in ksh

We have created a unix shell script to read a datafiles from specific input directory in Unix.
Users will be copying datafiles to the same input unix directoty.
During Testing we observed Unix Shell Script also read the incomplete datafiles which is still copying by the users.
As per requirement Shell Script should not read files which is still being copied/written.

any commnds to differentiate files which is in writing mode?

currently i have used "ls .csv" commnd in the script to list out all csv files which will be furhther veeing processed.But its also listing files which is still being copied/written.So i thought of differntiation such files by not selecting them for processing, to do so i can use mtime/mmin option.
mtime is good if i am slecting files which is not modified in hours.
but my requirement is not to slect files whose modified time is less than 5 minutes.So i would like to go for mmin.
i am using HP-UX(KSh) mmin is not working....
$ find . -name "14
.000" -type f -mmin +1
find: bad option -mmin

get this error
any idea hwy mmin is not working in HP-UX( Ksh )

always try search option.

thread.