Half life of MMI search result= 4 to 6 hours
http://www.google.com/search?q=+MM...:en-US:official&client=firefox-a

Bonus=
Carbimazole is rapidly converted to MMI in serum: 10 mg of carbimazole yields about 6 mg MMI
EXCELLENT reference
Werner & Ingbar's the thyroid: a fundamental and clinical text
By Sidney C. Werner, Sidney H. Ingbar, Lewis E. Braverman,
http://books.google.com/books?id=H...

Half life of PTU= 75 minutes
http://www.google.com/search?q=PTU...:en-US:official&client=firefox-a
This was a funny search result and informative . Looks to see who has the answer correct...took the time to google before being an on-line expert.(cough, cough )

Encyclopedia of Molecular Pharmacology, Volume 1
By Stefan Offermanns, Walter Rosenthal
http://books.google.com/books?id=i...
Also includes more on both ATDs for those interested.

Synthroid half life = 7 days
http://www.google.com/search?q=syn...:en-US:official&client=firefox-a


Psst.. .
Look under the PTU link with the multitude of erroneous answers, and notice our old buddy John /ithyroid) was perfect as expected. He may have had some of the more interesting ideas, but he was consistent in accurate research sources.