If it is working from the browser then it should work from the cron job, but may be your hosting is limiting the time of the executaion of programs from cron jobs, some companies limmit the time to save their servers resources so you may need to check with them. Also if you have telnet you can test from it like this:
perl Autoprocess.cgi password
Where the password is the one you set in the admin center for Auto process
That's the point. You need to ask them to remove this resitrictions for you. As for the time you need, you do not know as it depeneds on how many items will be processed, how many emails will be sent to bidders, sellers, how is your SQL server busy with other sites, how is the mail server is busy etc, etc. SO it has to have not time limit.