HACKED TOGETHER time limit for DB class midterm

Note this is to edx-west/rc, not master:

@jaericson 
Please review _thoroughly_ and test on your dev environment _thoroughly_.  If I don't get a thumbs up from you before say noonish tomorrow, then I won't release.

@nparlante can you be the second reviewer on this (also before noon tomorrow)?  I'll explain in email.