That is a weird delay. The inbound flight shows on schedule, but the continuation is a delay. Maybe they are subbing an aircraft and swapping something?
Anyway, this is the mirror image of my problem 2 weeks ago:
what is airport arrival best practice when intl flight delayed 2.5 hr?
(Hong Kong flight, but the other direction...) And yesterday's UA 180 was delayed a strange 18 minutes, notified the day before, despite the aircraft sitting on the ground since the previous evening.
At least you will be sure to qualify for delay compensation. Although from my 6 hour delay, it was a measly $200 coupon.