Originally Posted by
Ocn Vw 1K
If it's a "revenue" ticket, most/all U.S. carriers allow a free change or cancellation within 24 hours of booking. That one-day window is the last "free" time to troubleshoot dates and times on a non-refundable/changeable ticket.
If it's a US domestic carrier, US law
requires a free cancellation or hold for 24 hours from time of booking. UA uses the book & cancel option.