Originally Posted by
MatthewLAX
IME, the clock starts at time of purchase but if you call in, you have 24 hours after moment of ticketing.
This is my experience too ^
In fact, I've been able to get phone agents to cancel the ticket upto 23:59 the following day, but UA.com is definitely not set up to handle that.
Strictly speaking, the policy is 24 hours from time of purchase (
"clicking the purchase button", not time of ticketing), but agents seem to make exceptions frequently.