I am planning on running the game on my mac, but the timer suggested in the rules seems to be windows only. Is it alright if I submit times with real-time, or is there another way to record with portal time?

I don't know what you can and can't open on a mac, but I know you can retime demos after your run using this tool: https://www.dropbox.com/s/wnu2we07wtok0vt/Portal2DemoTimer.exe

Alternatively, you can manually go through all of your demos and add up the times.

You can also submit runs without game time, but I think you can't get a better rank than 105th if you choose to do so.

Try WINE (WINE Is Not an Emulator) - www.winehq.org If you can't be asked to use Terminal, you can just get PlayOnMac, which is a precompiled version of WINE. www.playonmac.com