I always buy Ritek 8x white printable discs and burn them at 6x, so each takes around 10 minutes or so.

I can burn faster but I find that gives the very best quality.

Also 250 gig is an awful lot to do in one go. If you have only one burner its best to give it a rest after every three or so to prevent it getting too hot.

Ideally you'd have dual burners so you can burn one in the top drive, then the next disc in the second drive to prevent overheating being a problem.