It's fiction.[1] "Artificial wormholes cannot be sustained for more than 38 minutes under normal conditions."[2]

[1] Quite enjoyable fiction. My canonically chronological SG viewing order for maximum enjoyment is available at https://docs.google.com/spreadsheet/pub?key=0AkwxWLA63pAmdG5...

[2] http://stargate.wikia.com/wiki/Wormhole_physics