Do one shots usually this long in begginer campaigns?

Hi. So me and my campaign were pretty new to DND but we wanted to start a campaign and play. So I became a dm since I had played a few DND sessions in the past and was more familiar with the game. So I read a couple of rule books to get more familiar with game mechanics and stuff. I chose for us the mines of phandelver since I've been told it's pretty good for begginer campaigns. So the day came and we started the first part of it(goblins arrows) which was supposed to be a one shot;the players chose a character and stuff and we started to play ... For 12 hours straight!! It took us 12 hours to finish a one shot and mind you I took into consideration them being begginers and gave them subtle hints throughout the game too. I was standing for the last 4 hours we had sit down for so long. And I was pretty curious, is this a normal thing?