Huygens Summary Timeline
This is a more-or-less arbitrary collection of events during the Huygens mission that are of scientific and/or engineering interest. Compiled by R. D. Lorenz drawing on the work of many. 
The  official UTC value of T0  is 2005-014T09:10:20.828 .
T-T0 Altitude (km) Event Ref
-16143 Probe power-on 1
-8396 Probe support avionics power-on 1
-348 Arrival at interface altitude (1,270 km)  3
-6.375 S0 (deceleration falls below 10 m/s2) 3
0 t0 (start of the descent sequence)  1
1.4 Pilot Chute Inflates 3
2.5 Back Cover Release, Deploy Main  3
4.9 Main Parachute inflates 3
32.5 Heat shield separation  3
45 Transmitter ON  1
50 GCMS inlet cap jettison  1
58 GCMS outlet cap jettison  1
62 HASI boom deployment (latest)  1
66 DISR cover jettison  1
90 145 ACP inlet cap jettison  1
143.6 Data Transmission Begins 3
~528 126 Spin Rate = 0, spin reverses 9,5
900 111 Main Chute Release/Stabilizer Deploy 1
903 Stabilizer inflated 3
1050 Anomalous HASI PWA data 4
1242 Anomalous HASI PWA data 4
1249 90 Maximum Spin Rate = -9.56rpm 9,5
1440 ACP Pump On.   SSP API data degraded 5
~1500 ~76 Minimum in Zonal Wind Speed Profile 13
~1554 GCMS Ion Source 5 Anomaly 5,6
1974 Radar altimeter power-on  3
~2000 62 Peak in HASI RP Electron Density 2
~2700 45 Radar Altimeter B locks (false) on surface 11
3440 ACP Pump off 5
~3450 36 Radar Altimeter A locks (false) on surface 11
~4650 ACP Pump On.    5
5150 21 DISR detects faint cloud layer 14
~5200 20 Radar altimeter B locks correctly  11
5310 ACP Pump Off 5
~6000 15 Radar Altimeter A locks correctly 11
~6685 11.5 SSP API-V begins to get pulses 12
6720 10.9 DISR detects faint cloud layer 14
~7500 7 Probe turns to move WNW 8
~8650 1 Probe begins to move to SW 8
8745 DISR surface lamp on 1
8842 0.14 Radar altimeters lost lock 11
8850 0.1 SSP Echo Sounder Detects Surface 10
8870 0 Surface impact  1
~8874 Dust cloud dies away 7
~8874-8879 Bouncing/Rocking motion of probe dies away 7
8887 HASI temperatures begin slow increase 5
9052 HASI Temperatures begin fluctuating 5
9103 SSP API-V Pulses resume 5
9532 HASI Temperatures drop ~0.2K 5
9550 Discontinuity in HASI PWA Permittivity Data 2
10125 SSP API-V Pulses cease 5
10128 HASI Temperatures jump ~0.15K 5
~10400 GCMS C2H6 level rises 6
10423 Possible Dewdrop detected by DISR Image 897 5,8
10787 Last HASI Temperature 5
~11000 GCMS CO2 and C2H2 levels rising 6
13203 End of Cassini–probe link  1
16031 Probe support avionics power-off 1
20559 Last signal detection by Earth-based radio 1
~20700 Estimated Battery Depletion  ~T0+5.5-6hrs 11
Ref
1 Lebreton et al., Nature 438, 2005, 758-764
2 Grard et al., PSS 54, 2006, 1124-1136
3 Kazeminejad et al., PSS 55, 2007, 1845-1876
4 Hamelin et al., PSS 55, 2007, 1964-1977
5 Lorenz Analysis of PDS archive -unpublished
6 Niemann et al., JGR, 115, E12006, 2010
7 Schroeder et al., PSS 73, 2012, 327-340
8 Karkoschka et al., PSS 55, 2007, 1896-1935
9 Sarlette et al., COMPARISON OF THE HUYGENS MISSION AND THE SM2 TEST FLIGHT
      FOR HUYGENS ATTITUDE RECONSTRUCTION, International Planetary Probe Workshop,
10 Zarnecki et al., Nature 438, 2005, 792-795
11 Couzin, Huygens Mission Post Flight Engineering Analysis, 
12 Leese et al., PPS 70, 2012. 28-45
13 Bird et al., Nature 438, 2005, 800-802
14 Karkoschka et al., Icarus 199, 2009. 442-448