Thank you @proteus-h ! For IOS devices there is a limit of 1/3 - 1 second exposure hard set so what the app is doing is adding/stacking images internally. This is an OK compromise, because at least you don't have to deal with hundreds of images on your hardrive to get a decent exposure.

Please have a go at taking some images through the phone, its a lot of fun! Currently I am doing the second part of this article which is imaging through a telescope. Hopefully, I'll get it posted next week sometime.