It's not likely you successfully burned a 50 minute DVD in 20 seconds. Something is wrong somewhere.
Meantime, I would suggest your not trying to burn a PAL DVD from your NTSC project. It's rarely a clean conversion.
In fact, virtually all European DVD players are capable of playing both PAL and NTSC discs. So I'd recommend you send your friend a regular NTSC DVD of yoru slideshow. It will play on his or her machine.
Meantime, I hope you're not re-creating DVD files every time you want a copy of your disc.
it's much wiser to select the option to burn your DVD to a folder on your hard drive rather than directly to a disc. Creating duplicates of your DVD are then as simply as using a program like the ImgBurn (free) to burn copies of your VIDEO_TS folder to discs.
Your burn did not work properly for some reason... but, all is not lost... many/most PAL players work with NTSC... email your friend and ask
ADDED... Steve posted while I was writing
Does PAL information take up that much less space on a DVD than the NTSC version?
When you were in the burn dialog of each burn to (NTSC) or burn to (PAL), what did the Quality Area of the burn dialog show for:
I find that I get the same space required and bitrate for the same Timeline content whether the burn to DVD disc project preset is
When you explore the properties readouts for your burn tos with different burn times, were there any differences observed.
If you take both DVD discs and explore them, opening to each's VIDEO_TS Folder/VTS_01_1,VOB, and playback that VOB on your computer player, how do the duration and content compare?
Were you multitasking when you were burning to DVD disc the one that had the longer burn time?
Just some thoughts for now.