What is the half life of injected insulin

There is not one answer for this because different formulations of insulin will reach peak levels at different times and the length of time that insulin stays active will vary because of anti-bodies to inusulin as well as metabolic factors. Having said that human insulin takes about an hour to peak and then is about half that peak within 5 hours. see http://care.diabetesjournals.org/content/7/2/188.full.pdf