Calendar alerts on iphone 12

Hi recently when I put an event in the calendar and try to set the alerts, when I set the first alert its good. But when I set the second alert, it gets saved in the 1st alert space. for example, I want the alert at 10 am. so I set it for 1 hour before. Then go to set the second alert at 15 mins before, but the phone switches the alert times so 1st alert is 15 mins before and 2nd alert is 1 hr before. Makes absolutely no sense.