On the one hand, timing something is about reminding myself "No, it's only been five minutes," but it is ALSO about knowing when something is taking way longer than it should.
If I'm put into an exam room in a doctor's office, I start a timer. Because I have been forgotten about in a doctor's office before, I get nervous that I'll just be sat in there forever, and the timer tells me "No, they haven't forgotten you, it's only been 10 minutes." But it also tells me if I have been there longer than appropriate (generally more than 40 minutes) so that I know when it's justifiable to flag down a nurse to find out what's going on.
At bag claim, because I know it usually takes about 20 minutes to get my bag, I don't get concerned until the timer passes the 20 minute mark without any bags appearing. At that point I know I need to take off my headphones and start paying attention -- looking at signage, maybe asking someone if I'm at the right carousel. Maybe don't worry yet, but start double-checking. Perhaps the delay is unavoidable and it'll just be an hour, but at least, having asked, I KNOW it'll be an hour, and the timer will tell me when the hour is past and I should maybe check in again.
Now, if the bags do start showing up before 20 minutes but my bag hasn't shown up by the 40 minute mark, I know that again it's time to put my head on a swivel, and at the 50 minute mark it's time to go speak to someone in the baggage claim office. This has more than once helped me locate my bag when it's accidentally been sent to the wrong part of the airport. There is no point at which, without the timer, I would go "man this is taking a long time" and then actually go ask, because I wouldn't actually know how long it had been.
The timer both prevents me from worrying before I need to and tells me when to start worrying -- essentially, because I'm both perpetually impatient and also infinitely patient, I've outsourced my patience to a stopwatch. And because I time a lot of things, I now know the average time a lot of things take, which helps me calibrate my concerns appropriately. Ten minutes is a long time to wait for a burger from McDonalds, but it's actually on the short end of the time it takes to get a burger from Shake Shack. It's not a long time to be on hold with the HR office of my old employer, but it's longer than I'd usually be on hold with my pharmacy. Et cetera.
I know I say this all the time but I still find it hilarious that I didn't know I had ADHD until I was forty years old.