How to slow down Time-Lapse video on iPhone

I love filming many things in time lapse, especially cooking food. But the time lapse video becomes too fast for longer videos. I read that the iphone automatically adjusts the frame rate to make all videos between 20 and 40 seconds. If i cook something that takes a long time, the video goes way to quick. I'd rather have a longer video that I can see what's happening.

Is there a way to manually adjust the frame rate on time lapse videos?

[Re-Titled by Moderator]