The vast majority of all Longs Peak climbers do so via the Keyhole Route. This route is 7.5 miles with nearly 5000' of vertical gain. Things can become a little fuzzy because there are many short-cuts to the trail below the Boulderfield, but the "cleanest" runs will be done sticking strictly to the main trail, which is well-established and obvious. The fastest ascent of Longs via the Keyhole (and sticking to the trail) that I have heard of so far is 1h41m58s by Anton Krupicka on June 8, 2012. His round trip time (including time on the summit) was about 3h15m.
Krupicka's time beat Kraig Koski's 1h49m, set in August 2000. Ryan Burch has done the round trip (sticking to the main trail) in 3h26m10s (ascent time of 1h59m) on Aug. 10, 2011. His trip report, with detailed splits is here. Fast times have also been reported by Bill Wright (3h35m car-to-car in Aug. 2000), and by Jeff Valliere (total time around 3h23m, 1h52m to the top, Aug. 27, 2010), but these were done using some of the short-cuts below the Boulderfield.
Krupicka ran up in 1h41m58s, "spent 30min on the summit", then ran down in a very fast 1h2m54s. He confirmed the rest time on the summit was "definitely no more than 30min" in an email to me. He also reported the following splits:
Ascent:
Goblin Forest, 14m45s
Battle Mt, 31m00s
Chasm Jct, 41m25s
Granite Pass, 54m05s
Boulder Field Shelter, 1h10m05s
Keyhole, 1h18m50s
Bottom of Trough, 1h25m30s
Start of Narrows, 1h35m35s
Summit, 1h41m58s
Descent splits were (after stopping watch at summit):
Bottom of Trough, ~1h57m
Keyhole, 2h02m00s
Granite Pass, 2h17m20s
Chasm Jct, 2h24m30s
Battle Mt, 2h29m50s
Goblin Forest, 2h38m25s
0.5mi to go sign, 2h42m25s
Ranger Stn, 2h44m52s