MPH has added a field in their API for a time since the last block:
I added "last_block" field at getminingandprofitsstatistics api as you requested.
It's unixtimestamp number.
Since the pool uses PPLNS, it would be smart to auto extend the interval until a block is found (or end it earlier), otherwise the user would lose all his earnings for the round.
The same applies for YIIMP-based pools as well - they also include "timesincelast" in /api/currencies, which should be used to determine whether the script should switch to next coin or not.