phrase at the earliest time in the day: 一大早 He said he'd call back first thing tomorrow.他说明天一大早他会回电话的。 I have a big report due first thing in the morning. He went to see Katy first thing the next morning. Let's meet first thing to decide what we're going to do. It's probably best to schedule your visit for first thing in the morning. See also
firstordinal numberdeterminer(BEFORE ALL OTHERS)
first thing | American Dictionary
first thing
idiom early in the morning: He said he’d call back first thing tomorrow .