Hyperlapse frm instagram has options for speeds. Check it out. Its free as well..
Thanks - I had checked that one because it's been written about quite extensively, but I didn't see any way to slow down an existing video (unless I missed it)
using iMovie (on iPhone) you can slow down an existing time lapse video:
just create a new movie, import the time lapse video, tab the video and select the second icon at the bottom to change the speed controls. You can change the speed slider to slow it down to 1/8th and speed it up max 2x the original speed