The London Marathon starts in less than 4-hours. Women’s elite start at 9:20 a.m. London time (4:20 a.m. ET/1:20 Pacific); men’s elite start at 10:10 a.m. (5:10 a.m. ET/2:10 Pacific).
TV / Streaming info is here:
http://www.letsrun.com/news/2015/04/2015-virgin-london-marathon-streaming-and-tv-information/
If you're in the US and don't want to get up in the middle of the night, learn how to watch without knowing the results here:
http://www.letsrun.com/news/2015/04/how-to-watch-the-london-marathon-without-knowing-the-results/
Tracking and results: