I'm sorry the site timed out before you could finish inputing your contacts. I can certainly understand the frustration. The site is designed to time out after 60 minutes of idle time. If you follow this FAQ it will also link to troubleshooting steps that can be taken if the site is logging you out under 60 minutes.
I also recommend, if possible, inputing the contacts in a spreadsheet first and then choose the "Upload From a File" option. This way, if the site does time out before you have uploaded them you can just re-select the spreadsheet.