I encountered the same problem. After struggling to get either datetime.strptime or time.strptime to work consistently without error I gave up and downloaded dateutil.
The dateutil module also has the benefit that you shouldn't need to work out the format string. Assuming that dateutil supports your date format your example code could be written as:
from dateutil import parser
obstimedt = parser.parse(obstime)
If you're interested in using dateutil then you can download it using this script: https://gist.github.com/4026516 (note that this script creates a 'temp' and a 'dateutil' directory alongside your Pythonista scripts - although the 'temp' directory gets deleted after download).