Here's the info on that specific flight:
Originally Posted by UAL.com
DEPARTS
City: Chicago, IL, US (ORD - O'Hare)
Scheduled Time: 1:20 p.m.
Scheduled Date: Mon., Dec. 28, 2015
Actual Time: 10:07 p.m.
Actual Date: Mon., Dec. 28, 2015
ARRIVES
City: San Francisco, CA, US (SFO)
Scheduled Time: 12:38 a.m.
Scheduled Date: Tue., Dec. 29, 2015
Actual Time: 12:42 a.m.
Actual Date: Tue., Dec. 29, 2015
Continued as UA2102 from SFO to HKG next day, leaving 1:05 p.m.
UA 869, the regular 747 flew about an hour later, also delayed half hour.